The New Big Boy on the Block: Ruger AR-556 MPR in 450 Bushmaster

There is a spot for big bores in most every gun enthusiast’s collection. For those who just like to burn powder at the range, hard-hitting rifle cartridges never fail to put a smile on the face of the person behind the gun. On the other hand, every hunter needs to have a gun that they can trust with their life when they go after dangerous game. Like many, I just so happen to be both of these guys. This made the Ruger AR-556 MPR 450 Bushmaster a good idea in my mind, but it needed to run through its paces to be able to take a place on the winner’s podium. I am happy to say that it performed well and gained bragging rights, but I’ll get into the details.

The Ruger AR-556 MPR 450 Bushmaster is packed with user-friendly features, making it a pleasure to shoot and it is sure to turn heads at the range. This rifle is topped with the Nightforce SHV F1 3-10 power optic for accuracy testing. The ammo tested was the Hornady 250 gr.

First of all, “Why 450 Bushmaster?” The answer to this question that many of you undoubtedly have is simple: power. The 450 Bushmaster averages about 2700 foot-pounds of energy at the muzzle. To put this in perspective, a 75-grain bullet from a 5.56x45mm NATO produces approximately 900 foot-pounds at the muzzle. This means that from basically the same gun it is possible to get 3x the power of a stout 5.56x45mm NATO. As mentioned earlier, this is a very big deal to those who may have intentions of hunting with this cartridge. In a matter of a second or less, this gun can produce 13,500 foot-pounds of stopping energy when using the factory-supplied five round magazine. Numbers are great and all, but here is a link to a video that demonstrates the difference in power between the 450 Bushmaster and the 5.56 NATO (similar to the 223 Remington) round.

The 450 Bushmaster is a cartridge that I would trust my life with while hunting dangerous game and the MPR is a rifle that I would trust just the same. This one had the opportunity to take an Idaho black bear and it performed excellently. You can read about my black bear hunt here at GunsAmerica’s Hunt365


Now the 450 Bushmaster round is great and all, but what about the rifle itself? If you want to read about the features that Ruger is eager to highlight, click here.

The features that I noticed right away and appreciated were a bit different. The rifle comes with a short muzzle brake on the end. This can be appreciated by any shooter that isn’t a bit masochistic. Next thing I noticed may only be picked up by someone who has built an AR in the past, but the handguard is not bolted to a barrel nut. Instead, it is clamped around the barrel nut. This stood out to me as a good feature because when you need to have a handguard line up with the barrel nut bolts, it often either takes shims or over-torquing of the nut in order to get everything to line up properly, and that just isn’t good construction. Moving rearward, I then noticed the Magpul furniture. The rifle is outfitted with an MOE grip which I found not only comfortable but handy for storing tax stamp paperwork inside for a suppressor. Also, it has an MOE SL carbine stock that has a flush cup sling attachment point which is complemented by another attachment point on the forward end of the handguard.

Overall, I was impressed at a glance by the construction of the rifle itself. It is also my understanding that the bolt construction is beefier around the lugs in order to ensure reliability when handling the bigger 450 Bushmaster round that it is chambered for.

The muzzle brake that comes standard on the MPR does more than enough to make shooting this large caliber pleasant but makes it no less impressive. Also, from this perspective, it can be seen just how slim the handguard is which makes for great ergonomics.

The particular rifle that I received was perfect except for one small flaw that I am willing to assume is unique to my particular gun. I noticed that the gas block was lightly in contact with the handguard. You may say, “What’s the big deal about that?” and my answer is as follows: The Ruger AR-556 MPR comes with a free floating barrel. This is conducive to accuracy because any kind of stress that is placed on the handguard is not transferred to the barrel. In a specific example, when a bipod is placed on a non-free floated handguard, it puts an upward stress that also pushes on the barrel and gives vertical stringing on the target downrange. Keep this in mind when I get to the section about this rifle’s accuracy performance.

The MPR comes with Magpul MOE furniture. This gives the rifle a high quality and sturdy feel when compared to the standard mil-spec type on most factory AR-15 style rifles.

The Trigger

I feel that the trigger is such an important part of the rifle that it deserves its own section to be discussed. I have shot the older models of the Ruger AR-556 and have been extremely underwhelmed by the trigger. However in this new model, the MPR, Ruger must have heard a few of the people’s complaints and paid special attention to this part of the gun. Props to Ruger as a company for doing this. The trigger is extremely impressive for what I would consider an entry level AR15. It is listed on Ruger’s website as a 4.5 pound two stage trigger, but because of its crispness and lack of creep, it feels lighter than some 3-pound triggers that I own. Consequently, I have no plans of changing this trigger out for an aftermarket trigger in the future, which I typically end up doing for most all rifles. Because of this in itself, the new Ruger AR-556 MPR puts a huge smile on my face and is a pleasure to shoot.


As mentioned earlier, I believe that my particular rifle may perform slightly less well in this area than the rest because of the gas block being in contact with the forend. However, I was not disappointed in its performance at the 100-yard line. I want to mention that my favorite shooting sport category is long range shooting, so I have extremely high standards on what a rifle should do. If you are like me, you may be hoping that I might say that this is a sub MOA gun. But I want to bring up something first: Consider what the uses of a carbine length, 45 caliber rifle could be. It could possibly be a truck gun used to punch holes through thick objects if the need arises. It could be used to hunt big game in uncomfortably close quarters where stopping power matters. It could also be used as a home defense rifle if a person wishes in order to stop threats in their tracks. It can fill all these roles, but long range is not one of them. Because of this, I decided before shooting the rifle that I would be extremely happy with anything that I could keep grouped in a dinner plate at 100 yards, and I promise it did better than that in the end.

The shot in the bottom right of the FTX Black is a sighter shot, not a flyer. The Hornady FTX black 250-grain ammunition produced a group at 100 yards that is 1.955 inches. In comparison, the Hornady FTX Custom 250-grain ammunition printed a group at 100 yards that is 3.248 inches. Both groups are 10 shot groups.

I tested the accuracy and reliability of the rifle with two different types of readily available ammo. These were both made by Hornady; the 250-grain FTX Black and the 250-grain FTX Custom. The cost of the Hornady FTX Black 250 grain 450 Bushmaster ammunition is listed on MidwayUSA for sale at $1.35/round. Also, the Hornady FTX Custom 250 grain 450 Bushmaster ammunition can be found for $1.45/round. Between both of these ammunitions, I had extreme reliability which is defined by zero feeding issues, zero ejection issues, and the like. I originally had a red dot sight mounted on this rifle to fit my ideal function. But for the test, I threw on the new Nightforce F1 SHV 3-10 power optic. The FTX black printed a 10 shot group at 100 yards that measured two inches. The FTX custom printed a sort of confusing 10 shot group that measured just over three inches but had 5 shots within 1/2 inch.

The MPR is as reliable as it is sturdy. I have beat the tar out of this gun in all scientific sense of the phrase. It has been on multiple bear hunting trips, beat around in a backpack for miles and drug through the dirt and foliage and managed to perform with zero malfunctions to date.

The Verdict

I am a fan of building your own rifles in order to get the quality and features that you want in a gun, but I must say that I am impressed with Ruger’s AR-556 MPR in 450 Bushmaster and I will be buying one for myself soon because of this. The rifle is constructed to handle the extra power that the 450 Bushmaster produces over the 5.56x45mm NATO round. It also is equipped with quality furniture, is lightweight and comfortable to shoot. The trigger is crisp and light and the gun itself is reliable. On top of it all, the accuracy that I would want this rifle to have is definitely there. If any of my friends were interested in owning a big bore AR-15 style rifle, I would be more than comfortable and likely to point them toward this particular model made by Ruger.

A must have for any gun collector or enthusiast, the new Ruger AR-556 MPR in 450 Bushmaster is a pleasure to shoot as well as look at.


Barrel Twist

1:16” RH


Black Synthetic, Collapsible


Free-Float M-LOK®



Barrel Length


Muzzle Thread





Type III Hard Coat Anodized


7.4 lb



Overall Length

35.60″ – 38.90″

Length of Pull

11.10″ – 14.40”





Street Price

≈ $800.00

***Shop GunsAmerica for your next Ruger***

About the author: Riley Baxter is an avid and experienced hunter, shooter, outdoorsman, and he’s worked in the backcountry guiding for an outfitter. He also get’s a lot of enjoyment out of building or customizing his firearms and equipment. Check out Riley’s Instagram @Shooter300

{ 19 comments… add one }
  • MojoMitch November 28, 2018, 9:33 pm

    I like it, yes yes!!

    Scotty, good to hear one can be built inexpensively too, thanks!

  • Michael November 18, 2018, 6:51 pm

    I’ve had 1 since they came out , this caliber is the most accurate and deadly hunting round I’ve ever used. I now have 3 of them and just killed the 90th deer of my hunting career this weekend. From ARs to bolt guns they just work buy 1.

  • Joe November 15, 2018, 5:52 am

    If I ever develop the need to kill aggressive engine blocks I will keep this thumper in mind.

  • RayJN November 14, 2018, 2:22 pm

    That is more muzzle energy than a 1600 fps 12 ga 1 oz slug

  • Johnny November 13, 2018, 2:58 pm

    I love my 450 Thumper! Loved the idea of the cartridge since 2008-ish, took me until 2013 to finally build one. 11 days after it was completed, and handloads (needed a lead free round, no factory non lead available at the time) tested and dialed in 4 days before I took it on it’s first hunt. I was getting 5 shot ragged holes at 100yds on the range off a rest. It’s first shot in the field dropped a trophy hog (~320lb 4.5″ cutters), not even a twitch when it hit the ground. Packs a punch, fun as can be to shoot and pretty amazing to get the accuracy you can get out of it with such a large heavy projectile. And of course the moment Commie-fornia bans mail order ammo all the good factory offerings for this round come out???! I wanna try em all!!!!!!!!!!!!!!!!! 🙂

  • Kane November 13, 2018, 9:43 am

    I like that tri-pod. I would appreciate any details Riley Baxter or any other respondent would provide on that item.


    • Riley baxter November 13, 2018, 7:22 pm

      I love it too! It is a Neewer carbon fiber tripod. I bought it when it was new, and at the time it was one of the cheapest carbon tripods. But sadly, Neewer caught on that they made a great product and almost doubled the price to ~$120. Still highly recommend it.

      The rifle grip is called a Pig Saddle

      Happy shooting!

      • kane November 14, 2018, 11:25 pm

        Yeah, I will probably cough up the money in part because there are not that many tripods that I like right now. Thanks for the info.

  • Scotty Gunn November 12, 2018, 6:42 pm

    Built one like this for a whole lot less. Match barrel. Even with a nice scope, came in way under $1000.00

  • Johnny Raygun November 12, 2018, 5:16 pm

    I, like most, always carry a range bag when shooting and testing. Inside that range bag, along with first aid kit, personal protection and bore snakes in every caliber, I bring common gunsmith tools. including Torx and Hex wrenches. It looks like the Ruger design allows for easy removal of hand guard. From there it is a question of moving the gas block. Depending,,, this could be as simple as a light hammer tap on the gas block,,,, until the rifle goes back to the shop. Good article, I like the the idea of that much power in a light carbine.

  • Ross Neal November 12, 2018, 2:11 pm

    I have an 18″ 450 BM Bear Creek upper and I love it. Can’t wait to hunt with it this year.

  • Bill 2 November 12, 2018, 10:00 am

    I hope everyone has better luck with this. I had a bushmaster .450 upper that failed in less than 20 rounds. Failure to extract-had a live round stuck in the chamber. Sent back for warranty repair and was eventually told they would have to replace or refund. Googling the subject shows multiple failures on .450 bushmasters-no I wouldn’t trust my life with one of these- took the refund but now have lots of useless ammo on the shelf. Should I take the gamble with a Ruger? ( Ruger hasn’t let me down so far) or stick with my proven Marlin 1895 thumper in 45/70.

    • Riley baxter November 13, 2018, 7:25 pm

      I would not shy from the Ruger. I literally put hundreds of rounds through it and had zero issues. On the contrary, a friend of mine had just finished his 450 BM “Build” like most people do… sadly, it does not cycle reliably or feed well… I think this is typical of an un-tuned rifle that was not made specifically to handle this caliber.

  • Bill November 12, 2018, 8:15 am

    A little disappointed in the accuracy especially since I have shot the ruger american in .450 bushmaster bolt action and they shoot .5/.75 inch groups at 100 with the hornady black.

    • jim November 12, 2018, 12:35 pm

      Bill, I know we all want really, really great guns, but comparing this gun to your RA is ridiculous. A semi-auto with an 18″ barrel, and you are not satisified with 2″ groups? Pretty harsh.

    • Riley baxter November 13, 2018, 7:27 pm

      I honestly believe that my particular gun performed abnormally poorly because of the small defect it had. That said, i’d Keep an eye out for other people’s accuracy reports and find an average.

      Although, i’d Have to agree with Jim’s statement…

  • Jon November 12, 2018, 7:33 am

    Very impressed with the 450 Bushmaster and 458 SOCOM. I started to build a SOCOM but when looking at the ammo prices I decided against the build. I have a Spikes Hellbreaker and a Bear Creek Arsenal side charging upper ready to go. I’m thinking of building it up for 6.8SPC.

  • Jay November 12, 2018, 7:27 am

    I don’t understand why they went with a 1-16 barrel twist since it is a handgun twist rate for most 45’s. Maybe to ease production cost and not have to make different production items to make the 1-24 twist, the 1-24 is far more than adequate for the heavy, short, fast moving bullets. I don’t think many will be using them as a subsonic gun as a 45acp carbine will do that far cheaper! Reloading this big guy is a big plus and I like the 225FTX, little bit more speed and distance and quite accurate at 250 yards, depending on the shooter. Like shooting a 45acp on steroids! These guys pack a nice recoil but very manageable! I like the caliber/gun, Col. Cooper strikes again! Big hand shake and thanks to Tim LeGendre, Bushmaster and Hornady, nice job!

  • Daniel Haneline November 11, 2018, 12:45 am

    I have a GLFA 18″ upper sitting on a PSA lower. I installed a $20 kaw valley spring kit w/slack adjuster screw and polished hammer-sear. Leopold .450 turrent 3×9 scope is mounted for optics. Purchased everything individually on sale, 1 piece at a time. Have a total of $875 wrapped up , minus mags and ammo, in a 100 yrd threeleaf clover maker. Very accurate to 225 yrds feeding Hornady black thru it.
    @ 300 yrds however, my pattern opens up to 3’x3′ !!
    Have tried custom ammo that’s $3.85 a trigger pull to no avail.
    Damn pistol bullets!

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