Gunfight Science: SBRs in 5.56 Suck – Buy a .300 BLK

To purchase an AR pistol in 300 AAC Blackout on, click this link:

While the 5.56 (left) has a lot of great capabilities, working well out of a short barrel is not one of them. The 300 AAC Blackout (right) might be a great alternative.

While the 5.56 (left) has a lot of great capabilities, working well out of a short barrel is not one of them. The 300 AAC Blackout (right) might be a great alternative.

I am not interested in starting a caliber war (this time at least), and I’m not one of those veterans that is now going to bitch about how my weapon wasn’t good enough. 5.56/.223 has killed plenty of people over the last 40 years, and the AR series of rifles works fine. I don’t care what a lost convoy of water purification specialists tells you. I am, however, telling you that the weapons system has limitations. Much like a car, you can’t just change things willy nilly and expect predictable results. You can build a hybrid Hummer or a diesel Prius, but that doesn’t mean you should. Many factors go into how a weapon functions and the ballistics of your chosen projectile. 5.56 is absolutely fine as a combat cartridge. As long as you can move the bullet fast enough.

I love AR rifles. I own dozens of them. One thing I do not own though, is a AR in 5.56 with a barrel length less than 16 inches. That has nothing to do with the fact that I am too cheap to get a tax stamp, or pin the flash hider on a 14.5-inch gun.

For anyone new to the AR family, here is a short but sweet summary. If you are actually interested in short-barreled rifles, seek legal counsel, not a guy that hits things with a hammer for a living. Here goes. The National Firearms Act of 1934 imposed restrictions on short barrel rifles ( SBRs), short barrel shotguns (SBS), silencers, and machine guns. For the purposes of today’s discussion, that means a rifle barrel must measure 16 inches muzzle to breech face, and the overall length of the rifle must be 26 inches (it is 18 inches of barrel for a shotgun, by the way). Provided a muzzle device is permanently attached (commonly called “pinned and welded”), it counts as part of the barrel for length. In theory, you could have a 2-inch barrel with a 14-inch muzzle brake welded on and still be legal. Insert your own 2-inch barrel joke here. If you want a barrel length below 16 inches, you must apply for a $200 Tax Stamp and register the weapon with the ATF. To me, it is a happy accident that the minimum legal length just happens to be my ideal 5.56 barrel length anyway. Why is 16 inches ideal?

Top, PWS MK114 5.56 pistol upper receiver, with Gemtech Patrolman 5.56 suppressor. Bottom, PWS MK114 300AAC pistol complete, with Gemtech GMT300BLK suppressor. Magpul BUIS on both.

Top, PWS MK114 5.56 pistol upper receiver, with Gemtech Patrolman 5.56 suppressor. Bottom, PWS MK114 300 AAC Blackout pistol complete, with Gemtech GMT300BLK suppressor. Magpul BUIS on both.

5.56 gets most of its lethality from velocity. This has been shown over and over again with ballistics gelatin, animal testing, and combat experience. Dr. Martin Fackler is famous for his testing of the 5.56 cartridge at various velocities while at the Letterman Army Institute of Research. I normally don’t put that much credibility into ballistics gel, but this is backed up by both my own time in combat, After Action Review (AAR) materials from other conflicts, and the first-hand combat experience testimony I gathered over my years as a soldier and instructor. To put it in the simplest of terms, 5.56 is basically a heavier, longer .22 LR. Above a certain velocity threshold, the bullet turns into a tissue blender. Basically, at above 2,700 feet per second (fps), as the bullet enters tissue, it turns 90 degrees sideways, and then can explode into little pieces. This causes massive tissue damage in what is normally called “secondary cavitation space,” and allows the little 5.56 to punch way above its weight compared to bigger bullets.

Alright, neat, so what? The problem lies in what happens below 2,700 fps. There is no mathematical certainty in anything related to terminal ballistics as there are too many variables, let’s be clear on that. But in a sense of stacking the odds, it works like this. At 2,700 fps and above, our bullet usually fragments. The faster it is moving, the higher those odds. Below 2700 fps, the odds of our bullet fragmenting start falling lower. And it’s not a straight-line loss either. Below 2,500 fps, it almost never happens. What does this have to do with barrel length? Every bullet ever built has an ideal barrel length to achieve maximum velocity. It is a complex physics equation related to powder burn, twist rate, friction, and gas pressure. My physics education consisted of “hurt people and break all their shit,” so we are just going to talk in general terms.

Science, it's not just for nerds. Pact chronograph, Gemtech suppressors, and American Eagle ammunition was used in the testing.

Science, it’s not just for nerds. Pact chronograph, Gemtech suppressors, and American Eagle ammunition was used in the testing.

5.56 was built to run out of a 20-inch barrel. That gives near ideal velocity and full powder burn, usually in the 3,100 to 3,250 fps range. Every time we cut the barrel off, we lose some amount of velocity, and it is also not a straight graph line. It also varies by some degree per barrel manufacturer. Cut to 16 inches, you start at the muzzle at about 2,850 fps with average bullet weights. Cut to 14.5 and you are generally around 2,650 fps. Cut to 10 inches, you are around 2,500 fps. This is where we run into problems. In a 10-inch barrel, you are already well below the fragmentation threshold at room distance.

So, what are we going to do about it? I’m not going to smack talk your choice of a short barrel. I’m also going to take the high road for once, and leave the mom jokes out of this. I have an AR pistol myself; there is a place for them. I’m just going to ask you to make an educated choice. The jury is still out on 300 AAC Blackout and its lethality, because it is so new comparatively. But it’s not rocket science to me. My velocity tests show Blackout to be 400 fps slower than 5.56 from a 10-inch barrel. It is also almost triple the bullet weight, and it starts as a .30 caliber. If you just want a gun to plink with, by all means go with the cheaper option. 5.56 is the clear winner there. But if you might ever need your gun to do men’s work, I suggest you cowboy up on caliber.

To purchase an AR pistol in 300 AAC Blackout on, click this link:

About the author: Clay Martin is a former Marine and Green Beret, retiring out of 3rd Special Forces Group. He is a multi-decade and -service sniper, as well as 3-Gun competitor and Master ranked shooter in USPSA Production. In addition to writing about guns, he is the author of “Last Son of The War God,” a novel about shooting people that deserve it. You can also follow him on twitter, @offthe_res or his website,

{ 92 comments… add one }
  • JR September 29, 2021, 10:22 am


    You wrote a follow on article, where you re-thought the effectiveness of the 5.56mm AR pistol/SBR, based on new ammunition designed for shorter barrels. This article seems to not be in the GA archive any longer. Could you re-post the article or publish a link?

  • Deputy Dawg August 4, 2020, 11:30 pm

    Yes yes Insert joke.

    The 5.56/.223 was tested thoroughly by our local SWAT team after an almost tragic episode with MP5s in .45acp. Travelling through suspect then walls almost hitting an innocent in adjacent apartment. Suspect survived too. Badass mofo!

    They found that The 5.56 was a better Choice in an SBR setup as it tumbles on impact and is less likely to travel through multiple obstacles and kill something you weren’t intending too. In this circumstance the lighter and a bit slower can kill. …Errr I mean stop the threat….. and not overpenetrate. These are close distances for entry team not snipers.

    IE best for home defense with family, dogs, cats, fish tanks. 65″ TV I love.

    I personally prefer 7.62x 51/ .308 for anything else. All these proprietary rounds are $$$$$. Unless the Military finally adopts one.

  • Charlie December 30, 2019, 7:47 pm

    One thing that you didn’t seem to consider in the article was the use of subsonic 300BLK and a suppressor on a short-barreled (8-10″) upper. Since you would be shooting subsonic, the barrel length would have no impact on velocity (you don’t really WANT the velocity to be more than about 1050 fps), and the shorter barrel means that your suppressor equipped 300BLK wouldn’t be much longer than a 16″ barreled upper without a suppressor. Put a brace on instead of a regular stock and it’s a “pistol” not an SBR so the tax stamp cost and government attention are avoided. If you want more velocity, slap a 16″ or 18″ barreled upper on, with or without that same suppressor and you are in the high velocity club again. I find that 2360 fps shooting Barnes 110g TAC-TX is about all I can get from my 16″ PWS upper though. Still, that is 1360 ft-lbs of energy from a 30 caliber projectile. That compares well to a 5.56 62g M855 at 2940 fps and 1190 ft-lbs of energy with a 22 cal projectile. Subsonic (1050 fps) and 220g is going to be about 578 ft-lbs, no matter whether you are using the 16″ or the 8″ barrel (the speed of sound is the same). Not a lot, but better at 100m than a 9mm bullet is at the muzzle, and a lot more accurate at that 100m distance than a lot of folks can shoot 9mm at 25m. Especially during a rapid fire sequence. In my opinion.

  • Nick Rodriguez July 2, 2019, 10:55 am

    If 5.56 sbrs sucked then socom wouldn’t be using them. There’s a reason alot of them love the mk18. 300BLk is good but more expensive for a supersonic round that performs just like 7.62×39 and when subsonic performs like a handgun. It has its purpose and I would love to get one eventually but 5.56 has been proven time and time again and I doubt the bad guys will sit there and cry about what caliber hit them when they’re laying in a pool of their own blood. For close to medium range 5.56 gets it done. If you want to hit further out get 308.

    • David March 10, 2020, 9:20 pm

      Exactly Nick. SOCOM I think is going to 12 in barrels now, going even past their normal SBR of 14 to 12, and achieving the same terminal ballistics/performance. Clocking muzzle velocity at 2500 and over with their new rounds.

  • Jeff April 5, 2019, 9:51 pm

    Who is this Nicholas Johnson grammar nazi? He knows a lot about writing but little about an sbr. A 62 grain sp is a fine round out of a 10.5″ barrel. If it can kill a 250 pound hog it can kill a human.

  • Fr0man March 29, 2019, 10:12 pm

    It’s all relative. 55gr 223 Gold Dots open up to .50 caliber from a 7.5″ and are easy on the wallet but for my money 6.8×43 will kick the crap out of 300blk and 5.56 from a 7.5″ barrel but you gotta bend over and pay for the PRI mags if you want it to run right.

    300BLK has it’s place with the suppressor crowd but it’s no thriller from short barrels without buying exotic Barnes bullets meant to open up even slightly below the 2,000fps.

    Go check out LWRC’ s UCIW where they did a massive amount of testing with 6.8spc from an 8″ barrel for the Saudi government.

    That’s an SBR that will END a gunfight even at 200M despite it’s tiny size.

  • Rick O'Shea September 16, 2018, 11:08 am

    Caution this is not intended for those of insufficient constitution.

    I can’t speak to the effectiveness on bipedal mammals, but I can as to quadruped ungulates (whitetails) and in my non imperical experience this absolutely holds true. Speed definitely kills and it’s even more effective when that speedy projectile is carrying mass. My personal hypothesis is that if the projectile upon impact can impart the majority of it’s kinetic energy to the semi viscous target(squishy mostly liquid mammal) while it’s trajectory is supersonic, a Doppler type shockwave is formed which will rupture tissue cells and disrupt organ function. I believe this is why some deer fall in a spasm before getting back up but eventually dieing when shot placement is not optimal; and when shot placement is good and kinetic transfer is sufficient you achieve near instantaneous incapacitation. As supporting anecdotal evidence to my theory I reference a video by Keith Warren near missing a whitetail doe with a 50bmg and still achieving an immediate incapacitation. if you want go to about 2:55 into the video to get to the point. Now to those who would say that this is not the same as a projectile impacting the target I would say you are correct but air is still a fluid that has mass and can transfer energy, just not as efficiently as a more viscous semi liquid but I believe the same principles of physics still apply. So in closing that any given weight projectile has an ideal velocity it should be propelled at but is not normally achieved; and it is also my belief that all projectiles need to achieve at minimum a supersonic velocity from the muzzle and be able to maintain that velocity for a give distance that shall determine the “Effective Range.” When the projectile is no longer maintaining a Mach velocity I would no longer consider it to be within it’s effective range; and for greatest effectiveness the projectile needs to continue at a Mach velocity post impact and continue as such for an undetermined minimum depth of penetration.

  • Caleb June 12, 2018, 4:25 pm

    There are so many expanding defensive roundscavailable. Why are you obSessed with FMJ?

  • segian October 30, 2017, 12:05 pm

    This is for Tom Horn (The American Service-Members’ Protection Act) The Hague can suck eggs. The U.S. of A. should act in the best interest of The U.S. of A. I am glad Clay did this one just for the comic relief. The comments are hilarious. By the way I am not an expert and have no opinion about the viability of any round for combat. Also I AIN’T an English major and could care less about my less than spectacular grammer. Rock On Clay!

    • Nicholas Johnson February 20, 2018, 5:26 pm

      Nationalist xenophobe much?

  • NRAinstructor1972 August 11, 2017, 3:28 am

    I think the only plus that 300bo has over 5.56 in an sbr/pistol configuration and suppressed would be that it’s bullet weight and subsonic sig sauer solid copper bullet seems to be a spectacular performer.
    It should be really quiet and knock said turds out of their socks in a close range environment…
    I have a sig m400 in 5.56 pistol configuration and am considering buying a 300bo upper separately but I have never shot a 300bo….any good recommendations as to the pros and cons would be appreciated….thanks all
    Also I was told by gemtec that my 9mm can will take 300bo subsonic rounds !
    A definite plus so I won’t have to spend additional funds, tax stamp, or time…because 8-10 month turnaround time should be criminal !!!!!!!

  • Patrick July 22, 2017, 4:20 am

    I never understand how ‘range’ creeps into the discussion of AR pistols. I have several, all of which are for home defense. Defense becomes offense when talking ranges measured in 10’s of yards. Would be hard to argue you were defending yourself from a target 100 yards away.

  • G Callen Sr. February 6, 2017, 8:19 am

    Well I agree with guy’s saying stick with 7.62×39 round; but he also failed to mention the .308 which in a lighter 150 grain weight is good for hunting and self defense. Personally I would never hunt deer or bigger with anything lighter in weight. As for Short barrel rifles or long barrel pistols they are for clearing houses and tight spaces. Tactical but not practical. My quickest go to gun for self defense or dangerous game lever action .44 magnum; gets the job done.

    • Nicholas Johnson July 28, 2017, 8:15 am

      He “failed to mention” lots of calibers. That’s because this article wasn’t about all the competitor calibers, it was about the shortcomings of 5.56. Also, fix your grammar, kid.

  • Carson Reek November 9, 2016, 5:32 am

    If your looking for a heavy hitter which you can still get cheap ammo for, don’t over look the 7.62x54R. Its an absolute sledge hammer and is def combat proven. One of my favs, and will put down anything in your sight as far as you can see. Def would not want to get hit by that round no matter how short your barrel is, but every round has its purpose and light weight and concealability is not one its best attributes.

    • Nicholas Johnson July 28, 2017, 8:16 am


      • Nicholas Nerd Johnson August 6, 2017, 10:04 pm

        You’re a nerd.

  • Russ H. October 26, 2016, 1:04 pm

    I get your argument but first… I too am a Soldier and have been in the Army/Army Reserve’s for over 38 years (over ten in SOCOM in SF). I’m also a retired State Trooper and a firearms instructor. As you may or may not know, SOCOM (SF, Rangers, SEALS, MARSOC, etc) are permitted generous leeway on their selection of weapons and calibers. So are most larger police SWAT teams. I’m also speaking about weapons selected for up close and personal work with short barrels. The preferred weapon of choice for nearly all of these entities 5-10 yrs ago used to be variants of the MP5 in 9mm, however, the platform of choice these days is the M16/AR15 SBR in 5.56. Why? More punch than the 9mm, longer range even with short barrels and they can carry the same amount of ammo. The 300 Blackout appears to be a decent round but it hasn’t caught on with any of these organizations, just like the 300 Whisper, 458 SOCOM and half a dozen other specialty calibers that were designed by former military personnel for the very purpose this article addresses. This generally is this is due to the limitations related to range – the bigger calibers are simply outperformed by the 5.56 as range increases (unless you fire them like a mortar). This makes these larger calibers limited to purposes generally under 150 yards, which puts them in a box. The other issue is the cost and availability of ammo – nearly two to three times that of 5.56 and fewer manufacturers. So, if you know you will only use the 300 blk for close range and are willing to pay the price of ammo – go for it. I like the 300 Blackout as do several of my friends, just know it too has limitations.

    • Nicholas Johnson July 28, 2017, 8:25 am

      First; “Soldier” does not get capitalized. This is English, not German. Second, “Army Reserves” is the plural, not “Reserve’s.” You’re clearly not intelligent enough to formulate an argument, so I’m not even sure why I’m wasting my time schooling you. Also, the selection of the AR platform by many of those organizations is almost certainly primarily a logistical consideration, not a practical one. If it were a practical one, surely they could find a caliber better suited to their specific needs than the ubiquitous and extremely specifically designed 5.56. 300 Blackout has not been around long enough to become as established as the NATO standard round, so comparing it based on performance alone is an apples-to-oranges comparison. (By the way, that caliber is based on the 300 Whisper, not wholly distinct from it as you imply.) Your argument about range is pure BS as the 5.56 is a notoriously bad long range performer as it does not have the mass to maintain velocity at extended ranges. You’re the only one here putting an enormous number of calibers in a “box.”

      • Eric August 26, 2017, 7:02 pm

        Wow, someone’s panties are in a bunch, turn that grumpy frown upside down cupcake, your shitty attitude negates your whole argument…dick

      • Pablo August 28, 2017, 11:22 am

        Dude you are a dick! Do you get a kick out of attacking others?

      • Nerdy Nick Johnson February 28, 2018, 11:46 pm

        Dang, who pissed in your cornflakes. He was being perfectly civil. It’s not his fault your wife gained weight.

        • Jacoban Mugatu April 23, 2018, 8:19 pm

          Go play airsoft. Dork.

      • Don Kemmann May 4, 2018, 12:00 pm

        Russ H is a retired trooper. What are you? The “Grammar Police”?

    • PapaGuido July 16, 2018, 5:46 am

      Russ, thanks for your service and your feedback. Live experiences in combat is necessary to hear about when it comes to these discussions. I’ve been fortunate to spend time with guys that have had combat experience similar to yours and Clay’s, and even someone hit by 5.56 & 7.62×39. They generally don’t get into the caliber arguments because of the “armchair warrior” nit pickers that split hair over grammar and don’t listen to the informed.
      Thx for passing along your knowledge. Many of us appreciate it.

  • JoshO October 25, 2016, 11:37 am

    Some valid comments to this article, most of them some variation on “you don’t have to use FMJ for HD (duh)”. But I look at it this way: if I were hunting man-sized game I would be using a bigger cartridge. I’ll take 6.8SPC or 300BLK over any bullet in 5.56×45 all day.

  • Shooter McGavin October 24, 2016, 8:19 pm

    Brown Tip (mic dropped)

    • clay martin October 25, 2016, 11:17 am

      well played sir, well played.

  • Scotty Gunn October 24, 2016, 5:28 pm

    Simple solution -handload 5.56 and use commercial hunting bullets. It’s not like I signed the Geneva Convention. (Neither did the US)

  • BillyBob October 24, 2016, 4:30 pm

    You Should Have Done Your Home Work First ! Here are FACTS you should LOOK AT ! THEN LOOK AT THE COST PER ROUND !Technical Information
    Caliber: 7.62x39mm Russian
    Bullet Weight: 122 Grains
    Bullet Style: Full Metal Jacket
    Case Type: Polymer Coated Steel
    Primer Type: Berdan
    Ballistics Information:
    Muzzle Velocity: 2396 fps
    Muzzle Energy: 1555 ft. lbs.Caliber: 300 AAC Blackout
    Bullet Weight: 110 Grains
    Bullet Style: TAC-TX
    Case Type: Brass
    Ballistics Information:
    Muzzle Velocity: 2350 fps
    Muzzle Energy: 1349 ft lbsCaliber: 300 AAC Blackout
    Bullet Weight: 220 Grains
    Bullet Style: Open Tip Match
    Case Type: Brass
    Ballistics Information
    Muzzle Velocity: 1000
    Muzzle Energy: 488Caliber: 300 AAC Blackout
    Bullet Weight: 150 Grains
    Bullet Style: Full Metal Jacket
    Case Type: Brass
    Ballistics Information:
    Muzzle Velocity: 1925 fps
    Muzzle Energy: 1234 ft lbCaliber: 223 Remington
    Bullet Weight: 77 Grains
    Bullet Style: Sierra MatchKing Hollow Point
    Case Type: Nickel Plated
    Ballistics Information:
    Muzzle Velocity: 2750 fps
    Muzzle Energy: 1293 ft. lbs.Caliber: 223 Remington SUBSONIC
    Bullet Weight: 77 Grains
    Bullet Style: Hollow Point Boat Tail
    Case Type: New Brass Cases
    Ballistics Information
    Muzzle Velocity: 1050 fps
    Muzzle Energy: 188 ft lbCaliber: 223 Remington
    Bullet Weight: 53 Grains
    Bullet Style: V-Max
    Case Type: Brass
    Ballistics Information:
    Muzzle Velocity: 3465 fps
    Muzzle Energy: 1413 ft lb
    Sectional Density: 0.151
    Ballistic Coefficient: 0.290

    • BillyBob October 24, 2016, 4:38 pm

      They changed the order and combine muzz with the name of the next round !

  • Aim Protection October 24, 2016, 4:14 pm

    Your aurgument is based on the difference in the leathaity of a 5.56 running at 2500 fps /or/ 2700 fps- all due respect but that is laughable. You would be just as dead either way and I beg to differ with you on the bullet lethality. Maybe the round in question won’t fragment at 2500 fps but they have seen through test to still start the buzzsaw effect at 2500 fps which does the real damage and can actually be more effective than small fragmentation. Case closed…

    • clay martin October 25, 2016, 11:19 am

      Buzzsaw effect? I think me and Dr. Fackler missed the memo on that one.

  • Lou Gots October 24, 2016, 4:10 pm

    Which cartridge are you going to be able to get under more conditions?

    “Amateurs study tactics; professionals study logistics.” Military maxim, frequenly attinut4ed to Erwin Rommel.

    • clay martin October 25, 2016, 11:20 am

      That one is frequently attributed to Napoleon as well.

    • Nicholas Johnson July 28, 2017, 8:27 am

      The article is about lethality, not logistical availability. Get out of here with your red herring.

  • charly October 24, 2016, 3:28 pm

    might i suggest the author and 556 haters stand in front of a sbr , take a round ,then tell us how ineffective it was.

    • Aim Protection October 24, 2016, 4:16 pm

      If there was a like button here I would have hit it for your comment ….

      • BillyBob October 24, 2016, 4:50 pm


      • SBR_GUY November 5, 2016, 9:13 am

        I second that.

        I own several SBR’s.

    • Nicholas Johnson July 28, 2017, 8:28 am

      Might I suggest you fix your grammar and GTFO of here with your BS proposition. How about you stand in front of a .300 BO instead?

    • Cymond November 29, 2020, 2:55 am

      Might I suggest you stand in front of a 22LR and tell me how ineffective it was?

      “Effective” is not the same thing as “I really don’t want to get shot at all.”

  • Charlie October 24, 2016, 3:05 pm

    Ever noticed that rifle caliber that the US military has adopted for military use has become an excellent caliber for many if not all sporting and protection use in years past? Must have something to do with the fact they are the best choice . I will stick with what has been combat proven..223/.556.

    • BillyBob October 24, 2016, 4:51 pm


  • Brian October 24, 2016, 2:51 pm

    You should do some chrono’ing. I get 2800+ out of 11.5″ with xm193. I consider this sbr effective to 75-100yd.

  • BRASS October 24, 2016, 2:41 pm

    I don’t see the need or usefulness of a pistol length barrel or stockless configuration AR in a PDW. However, to imply anything less than 16″ doesn’t work effectively is false and foolish.
    The US Marines were the first to adopt the 14.5″ barreled M4 Carbine for MARSOC, FORCE RECON and some infantry forces and now the first to adopt it for all Marine Infantry. Marines adopted both a 10.3″ barreled MK18 unsurpassed and suppressed with the appropriate buffer groups for MARSOC use.
    While the Marines do a fair amount of test and evaluation of different weapons platforms for a variety of uses, they are not in the habit of selecting weapons that don’t function well for their intended purpose as standardized issue.

    • clay martin October 25, 2016, 11:24 am

      Actually, sometimes they do. I went to OIF 1 with an M16A2, because the USMC didn’t believe in optics yet. And yes, the Force Recon assault platoon had 14.5″ then, the sniper platoon had A2’s. The Army was actually first to adopt the 14.5 or M4 carbine for general issue, starting in 1996.

      You can kill someone with a slingshot if you do your job correctly. My point is 16″ is better.

  • Dillom October 24, 2016, 1:53 pm

    I was going to say….why does it have to be an AR and why does it have to be a .300? We all know of a .30 caliber cartridge thats very popular, very cheap, readily available, combat proven, and reliable….7.62x39mm!!!!! Wont say its the best (its not) but its my preferred caliber for a civilian carbine for sure. Disagree all you like but you cant argue with the fact that the most popular rifle of all time is chambered in this round.

    • Nicholas Johnson July 28, 2017, 8:33 am

      First, learn the apostrophe; it is your friend. Second, the author seems focused on the AR platform which does not operate well with the 7.62×39 round. The fact that the guns that fire this round are common is not an argument in its favor. Does the fact that Camrys are popular cars mean they are the most powerful cars?

    • Pink_Vapor December 11, 2017, 3:29 pm

      The angle of the 7.62×39 case wall causes excessive bolt thrust in an AR.
      Great combat round, not in an AR.

  • dward October 24, 2016, 12:45 pm

    I often think that some people responding and even some authors of articles get their ‘ballistics knowledge’ from Fallout 4. arghh

  • Bryan October 24, 2016, 11:17 am

    How about using an ak47 style sbr or draco with a brace. Proven .30 round that basically matches 300 blk. Performance. Much cheaper ammo, more relible……we atre talking cqb, not punching paper.

    • 33Charlemagne October 24, 2016, 1:00 pm

      Exactly! And since the recoil spring is in the receiver rather than the butt stock an AK with a standard length barrel equipped with a side folder stock can fold down to a mere 25″ seconds.

  • BillyBob October 24, 2016, 10:40 am

    H&K 51K 308 will but them down and roast them in one blast !
    6.5 creedmoore or 50bmg reach out and touch someone ! 300 zeroed at 100 drops 38\” at 200 !
    300 AAC Blackout is a fantastic hunting round. So long as your target isn’t much over 100 yards, that is. While having a chunky projectile is a nice improvement over the standard 5.56 cartridge, it does mean that you lose some muzzle velocity. And in turn, the trajectory past 100 yards for this gun has been described as “rainbow-like.”
    I’m not saying that it can’t be done. I’m regularly singing steel at 250 with my 300 BLK rifle, with a nice +3.4 Mil hold. But that’s not a shot I would be comfortable making on wildlife. Not humane.

  • Paul October 24, 2016, 9:47 am

    Or you could just use better bullets than FMJ

    • Dillon October 24, 2016, 1:56 pm

      He’s talking about a combat weapon and his time in the service and the experience he acquired there where FMJ the only choice.

      • Cymond November 29, 2020, 2:57 am

        Well, if we’re limiting our options to service weapons, then 300 Blackout isn’t an option, either.

        If his experience is limited to FMJ, then it is of limited relevance, too.

    • Drej October 24, 2016, 3:10 pm

      completely agree there Paul, If you aren’t required like the military to use FMJ there are countless amazing bullet manufacturers where you can get a bullet to do so many things at so many different velocities. Well Said Paul.

  • Kyle Newman October 24, 2016, 9:10 am

    Your whole argument is based on the performance of fmj out of a 10.5″ barrel. This is all geared towards civilians wondering what to buy, not military. We can all use whatever ammo we want. Hunting and self defense rounds don’t stop performing below 2700 fps. Also, ever heard of an AR pistol? With the “braces” available today, you’d have to be an idiot to choose to pay $200 for an SBR stamp.

    Some of you bashing 300 blk say 110gr is puny. They hit deer like a hammer and drop them fast. It’s the best home defense load on terms of suppressability and carnage caused. Like all 5.56 arguments, just use the right bullet.

  • J. Smith October 24, 2016, 9:09 am

    Food for thought.
    I was looking for a new PSD setup and did some tests. I started with several theories about what would work so i did some testing. I tried custom .300 blk ammo in super and subsonic values; 125 tnt (super), 208 A-max (subs) giving the best results. A half grain more or less in The 125’s and the rounds get squirrelly, but penetration and terminal damage were optimal, better than 150’s and other rounds.115’s were too costly and decided against Them. 208 a-max did not yield great accuracy nor good ballistics. You must know exact ranges past 25 yards to get even reasonable precision. Penetration caused yaw. All With/without supressors, in 7.5″, 10.5″ and 16″

    Then i tried a ps90 combo with 40g vmax, and a 57 pistol. Pistol sucks, just a lot of blast. But the ps 90 held promise, 50rd cap, decent accuracy with a fast fire, light, compact, easily concealed and maneuvered. Obvious choice, secret service uses p-90’s for psd, so…then i added up the cost and also what if it is a shtf Gun? Why dont i just go with a sbr in .223 and use 40g v max that out of a 7.5″barrel will exceed 2600fps depending on brand, they Reach near 4,000 fps in. 24″. Hmmm, maybe were on to something, same size weight as a 5.7, 40g and they are rated to 250m. I have killed deer with .223, 40g v max in. 26″ single shot, head shots only. The brains turn into pudding, they penetrate enough but dont overpenetrate and as the writer mentioned, they do fragment… Just a bit. So, collateral damage is minimal but terminal ballistics are amazing. Wound cavities are huge and penetration is sufficient. Add a suppressor or cqb device and the blast is tamed. Additionally, i tested and eventually Added to the set, 60g v-max (super) 55g tap penetrator, and 60g v-max (subsonic) for true suppressor use. One p-mag drum of each contingent. Using common mags, common caliber. You have an effective sbr setup that will rival any 300 blk setup, and yes, in a pistol length barrel.

  • Jon H. October 24, 2016, 8:10 am

    Good article and you make some very good points. All the comments are also valid when considering the choice in general terms.
    However, I offer this. Go out to your garage and open your tool box. Does it only have one flat blade screwdriver in it and absolutely nothing else? Guns are tools and as such different ones are better suited for different jobs.

    I have multiple SBRs (5.56, .300 BLK and even a 7.62X51). Each one works better than the other in certain situations and each one has general advantages and disadvantages (weight (both gun and ammo) terminal ballistics and sound signature). I suppress all of my ARs, even my .300 Win Mag NEMO and sound signature is a consideration, depending on the work you are doing. If you are clearing rooms and you don’t want the rest of the building rolling in on you after the first shot, 300 BLK is the definite choice. All others will go supersonic and you will get a crack the equivalent of shooting an un-silenced .22, which is not quite at all. If you only consider terminal energy, I highly recommend my 12.5 inch 7.62 SBR. I guarantee it will kill the $h!t out of anything you shoot with it, but it is heavy and loud, even when suppressed. But a MK18 upper (10.5 inch) has been used by the Navy and Army Tier 1 operators for a long time and it is tried and true. Just don’t expect it to be as quiet as a 300 BLK.

    That being said, your article does highlight why the groups mentioned above tested and used the 6.8 SPC and why the 300 BLK was developed.

    So, if you can own only 1 SBR, you have a tough decision to make and I feel bad for you, because no gun is perfect.
    That is why I recommend having one of each. 🙂

  • Dtwalkerfl October 24, 2016, 8:06 am

    Key word “subsonic”. 300 bk is super quiet around 1000fps. 5.56 subsonic is nonexistent.

    • J. Smith October 24, 2016, 9:19 am

      Yes, .223 subsonic exist and cheaper than .300blk in most cases, unless your shooting really crappy reman garbage. And, yes, it is very effective.

      • Charlie December 30, 2019, 4:47 pm

        Oooh ! Subsonic 5.56. Yeah, real deadly. Same degree of deadly as 22LR, which IS deadly but in much the same way that a sharp stick or pocket knife is deadly . . . . . .
        You are comparing grapes to watermelons.
        A 55g-80g 5.56 projectile moving at the same subsonic (1050 fps & 134 – 196 ft-lbs energy) is TOTALLY outclassed by a 220g 300BLK moving subsonic (1050 fps & 538 ft-lbs energy). I agree that neither one is much good for anything beyond 150m though.

  • ToddB October 24, 2016, 7:53 am

    All these short barreled guns seem cool. Guess they do have some place. If you need something that short and handy. But the author is right, they do lose a ton of velocity. And are beyond loud. I see people buying 308 SBR, guess they dont need hearing. I have a Australian Auto Arms T2 pistol. Yea you can carry it around under a coat, but the only reason I would use it. That velocity loss can be somewhat made up with ammo. Some say 55.56 is cheaper and easier to get than 300AAC. true but most of the cheap 5.56 is stuff that needs that high velocity to do a good job. As the military found out in places like Somalia, those shorter barreled carbines past 100yds or so just dont put a man down reliably, like a longer barreled rifle. They tend to just zip thru without the explosive effects 5.56 is known for.

    The 300AAC really is more of a suppressed thing. Yes it can shoot supersonic, but are sort of restricted to 110gr ammo. Its funny people who would say a 30-30 is inadaquate past 150yds for deer, say the 300AAC which has LESS velocity is good further out. A look in the reloading book, and a 300AAC starts out slower than the 7.62×39. You need a 110gr in a 300 to get the same velocity a x39 gets with a 123gr. I can see where 150gr would be even worse.

    I have been debating an upper build. I know a guy who says the 300 is the only thing to get. Im not completely sold on it. Only real advantage seems it fits in existing mags and bolts. At the prices they are getting, I cant see yet another caliber to stock up on, or sitting down and loading a big pile of it. Im leaning towards the x39, but there are the reliability issues, and the fact there is no off the shelf subsonic ammo. I load alot of subsonic, but for single shot/bolt guns. Making my own requires buying a bunch of new brass as there is little once fired stuff to be had. I can get 230gr cast to stabilize subsonic in a mosin which is the same twist as an AK. Trick would be a load that would cycle an AR.

  • jimmy james October 24, 2016, 7:10 am

    77gr projo doing 2500+fps out of a 12″bbl is good enuff for me. Would like to hav an SBR in 300BLK but logistically speaking an underfolder AK makes more sense.

  • mike October 24, 2016, 6:52 am

    Personally, figure the fact that nearly everyone I have ever met who is actually expecting to use his gun in a gun fight for personal defense is doing so mainly as a prep for drastic social upheaval that looks to be on the horizon. As such I would consider the ammo that is most readily available and easily transported to be far superior to the one that makes the most damage. That is undoubtedly in my experience going to be the 5.56/223.

  • Joe October 24, 2016, 5:27 am

    Buy this, no buy that…Bah Humbug….
    Short barrel AR, duhhh….Ain’t that what they make pistols fer….
    Seriously folks, the 300 blackout is an invention looking for a need.

    • paul October 24, 2016, 11:40 am

      Looking for a need? There are plenty of them. You can shoot hogs all day long with .223 and watch them run off into the brush. I’ve got plenty of pics of 200+ lb. hogs shot between 50 and 150 yards that dropped within 20 feet of P.O.I. with my AAC 300 B.O. pistol. It’s also great for small acreage hunting without the worry that your round such as .308 or 30-06 is going onto your neighbors property. Seems like the “ho hummers” of the .300 BO round are just too old or to cheap too cheap to accept something new. As for the “stamp”, it’s worth it so you can have an adjustable stock rather than looking over your shoulder and worrying a game warden or some other L.E. official will think you are shouldering your pistol.

      • Joe October 24, 2016, 5:11 pm

        Were those hogs packing heat or just switch blades ?
        My 308 hog gun gots to know….

  • Vince Black October 24, 2016, 4:18 am

    I “used” to have a 10.5-inch 5.56×45(sig factory 556 sbr). It was worthless with anything but expensive specialized hollow-point ammo. Too loud to shoot without plugs and muffs. I really wanted to like it and it did cycle well but the barrel was too short and the whole gun was poorly made. Short barrels have no place on a practical use .223/5.56x45mm (there are much better choices as we are not stuck with nato standard calibers). 7.62×39 works ok at 10inches but is best kept at around 12inches(think draco). Used to have a 10′ 7.62×39(Yugo m92) It was heavy in a balance-hurting sort of way and hard to make good hits with.
    9mm or 300blk is what you want for a short barrel gun. 9mm(mp5, evo 3s1, mpx) for 0-50m home use. Then grab the 8-9′ 300blk for outdoor adventures. I love my little 8′ 300blk is runs great. Do note that lighter bullets works better in short 300blk barrels. Stick to 110-125g bullets for 8-9-inch guns. There is some really junky 150ish-grain FMJ ammo out there for 300blk. That stuff is for SBR punching paper only. Have fun!

  • STEVE HOLTER October 24, 2016, 4:10 am


  • jack October 24, 2016, 4:05 am

    As for the use of the hollow points and the Hague Convention, #1. We are not a signer of it.(USA) and #2 We use the term “Open Tip Match (OTM) to make it a feel good round we use in many including the sniper rifles today.
    In the 7.62×51 using the 175gr sierra Match King bullet it is called OTM in military verbage and HP for us civilians. In the 300 Win Mag it is a 190 Grain again Sierra Match King OTM and the navy and some Spec Ops groups are using a 210 grain HP as well. Going larger caliber just means it goes much faster and still has that OTM tip on it except the Big 50. It only needs to hit the baddies and they understand they have been hit.

  • Mark N. October 24, 2016, 3:13 am

    Why would anyone own dozens of ARs? Isn’t easier to have a couple of lowers and as many uppers as your heart desires? Other than fairly minor weight differentials, and differences in triggers, if you’ve seen one lower, you’ve seen ’em all.

    • rogertc1 October 24, 2016, 6:25 am

      I have 7 ARs. Lowers like uppers can be all different. Just made an AR around a Spikes Jack . Just because you can’t or don’t does not mean the anyone else can.

    • Kyle Newman October 24, 2016, 9:19 am

      And the newb shows himself. If you knew anything about building precision rifles, carbines, or AR pistols, you wouldn’t ask such a dumb question.

  • Gary B October 24, 2016, 3:01 am

    I don’t care about the bullet fragmenting, I have my and my wife’s pistols with 8.5 inch barrels in 5.56. They are a good bit more lethal than 9 MM 5″ pistols and I have 28 of them to repel boarders. I have a supply of 5.56, none of 300 BO. I don’t see it as a problem.

  • TX October 23, 2016, 9:14 pm

    First, in a emergency scenario, 5.56 is much more readily available.
    Second… 10.3″ colt commandos and MK18s have killed plenty of bad guys…
    Stick with the 5.56, and the side bennifit is you don’t have to worry about accidentally blowing up your other 5.56 with a misplaced 300BLK projectile.

  • Will Drider October 23, 2016, 6:28 pm

    I appreciate the article and understand the process and decission. The article really applies to barrel length arguements for SBR’s and AR/AK style pistols. You talk about “mens work” but are vague. How many combat load mags are you implying? Speaking as a average Joe with limited resources, I can sure stock a hell of a lot more 5.56/.223 than .300BO. The receiving end of the Men’s Work will not think its plinking ammo, honestly; would you?
    If barrel length, over all length and velocity were the driving factors, gas piston would rule: add barrel length not stock for highest velocity in smallest package.
    You mention the 300BO being 400 fps below the 556 from 10 inch barrels like its nothing but add that 400 fps to the 556 and your in 16 inch barrel veloicity range. You leave bullet weight behind the curtin.
    What the 223/556 really needs is a powder that burns better and more completely in shorter barrels to deliver origional velocities. Call it +P PISTOL.

    • Brad October 24, 2016, 11:23 am

      “What the 223/556 really needs is a powder that burns better and more completely in shorter barrels to deliver original velocities.”
      We have that now, it is called the SOST round. Federal 62gr Mk 318 Mod 0 OTM. USMC and other Federal entities (not the big Army, they went with the M855A1) currently field this ammo. Improved powder burns completely in 14.5 inches of barrel, getting past the 2700fps threshold in a carbine. (~2950 fps at the muzzle). Round has improved intermediate barrier performance, as well.

  • JO3HN Thethreeissilent October 22, 2016, 3:10 pm

    I just have two things to say about your article on the merits of the 5.56. 1) AMEN and 2) I like you. I am a disabled, Vietnam MARINE CORPS VETERAN. She thanked me for my service and I said, “Your welcome, ma’am,” but I left out that I was sorry that I went and would never go again and if asked I would advise against it. People that make sense are in short supply as compared to those that just make cents. If you have to ask, you wouldn’t understand and if you understand, YOU DON’T HAVE TO ASK!

  • Dave Hicks October 22, 2016, 10:03 am

    I bought my 1st AR 15 in 1975 ,a COLT SP1 in .223 and I have owned a AR 15 in .223 off and on since. .223 doesn’t need a hollow point bullet to be effective,it’s fast enough and yes it works.

  • Tom Horn October 21, 2016, 9:44 am

    Is “Full Metal Jacketed” ammo dumb as a defensive round in 5.56? Is the Hague Convention of 1899 dumb? Yes. Luckily, it does not apply to me as a U.S. civilian.

    • Caleb October 23, 2016, 1:10 am

      The US was not a contracting party regarding the use of hollow points in the Hague Convention.

      • tom Horn October 23, 2016, 2:58 pm


        You are right. We are not bound to the 1899 Treaty as a signer, but by the decision of International Law at the Nuremberg Trials, post WWII.

      • Mark N. October 24, 2016, 3:09 am

        And it only applies to conflicts between signatories. Our current enemies of choice, the Taliban and ISIS, are non-state actors and non-signatories. Even if we were a signatory, we would not be required to comply with the FMJ edict. But we do. Something about morality, me thinks.

        • Tom Horn October 25, 2016, 9:52 pm

          “The Hague Convention of 1899 says:
          The Contracting Parties agree to abstain from the use of bullets which expand or flatten easily in the human body, such as bullets with a hard envelope which does not entirely cover the core, or is pierced with incisions.

          This Declaration was not ratified by the United States, but… “After World War II, the judges of the military tribunal of the Trial of German Major War Criminals at Nuremberg Trials found that by 1939, the rules laid down in the 1907 Hague Convention were recognized by all civilized nations and were regarded as declaratory of the laws and customs of war. Under this post-war decision, a country did not have to have ratified the 1907 Hague Convention in order to be bound by them.”

          Suppose it would just depend on who was prosecuting you for a war crime.

          and yet:

  • Sean October 20, 2016, 4:04 pm

    Or just shoot 7.62×39 and enjoy the ridiculous amount of money you save over .300 BLK. 🙂

    • jack October 24, 2016, 11:09 am

      Ya. That’s what I was thinking too. Although the Anderson M4 looks mighty inviting.

    • Charlie December 30, 2019, 7:25 pm

      Well, when comparing prices for 7.62×39 and 5.56×45, when you are planning to just buy inexpensive but reliable commie ammo (like TulAmmo) both of them cost the same: 17¢ per round. So don’t let the price deter you from the caliber you prefer. If you want 300BLK, that is 43¢ per round, although I can reload it for 26¢ per round if I have the brass. Depending on your financial situation, that doubling of the cost per round would deter a lot of guys that looking to lay in a serious ammo supply at the homestead I reckon. Fortunately, I understand that TulAmmo is about to start selling 300BLK ammo to us capitalists this winter (2019-20). Hopefully they will bring that price down for us by selling bulk steel-cased 300BLK ammunition. AND, they may force our own manufacturers to reduce their prices to match them. . . . . or get close anyway. I have considered 7.62×39 and one or more weapons to shoot it with, but I haven’t made a decision yet. I already stock considerable 5.56, 308Win, and 300BLK. I’m not sure I need another caliber and the guns to use it.

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