How to (Legally) Build A Short Barrel Rifle

This Aero Precision upper receiver and barrel is going to make a really nifty short barrel rifle one day.

This Aero Precision upper receiver and barrel are going to make a really nifty short barrel rifle one day.

As defensive weapons, rifles rock. They’re easy to shoot accurately unless you’re into torching off .577 Nitro Express cigar cartridges. With box magazine designs like the those of the AR-whatever families, capacity is great, and reloading is easy. In fact, the only real downside of a rifle as compared to a pistol is maneuverability and portability.

The Skinny on the SBR

Enter the short barrel rifle, or SBR as we’ll say from here on out because we care about saving the electrons. With its compact size, an SBR can be plenty handy for a car or home use. An SBR has most of the benefits of its larger counterpart, minus a bit of velocity, but with half the calories.

The MCX Rattler SBR.

The problem is that SBRs are a royal pain in the butt to understand from a legal perspective. With the passage of the 1934 National Firearms Act (NFA), they are restricted items. To make, buy, and own one, you’ll need special permission from Uncle Sam by completing and submitting a Form 1, and you’ll need to purchase a colorful and ornamentally pleasing tax stamp that will cost you $200.

Want an SBR of your very own? Never fear, we’re here to make the process easy for you.


I’m not a lawyer, and I don’t play one on TV. Besides, if I were going to play something on TV, I would be a skydiving Kingsman in a Zombie movie, not some guy who sucks the fun out of everything wholesome and good.

Anyway, the law that governs the short barrel rifle market was written in 1934, before the invention of electric guitars, ballpoint pens, and Tupperware parties (yes, look it up.) As a result, the ATF has to do all sorts of weird legal interpretation as the law didn’t account for the myriad of firearms options we have today. Simply put, the law has no provision for modular systems like the AR-15 that can be built into rifles or pistols and have practical attachments like chainsaws.

Navigating this process, we’re faced with the original NFA law and subsequent laws, which are comprised of billions of pages of pages of gibberish dictated by inebriated politicians. Then there are policies issued by organizations like the BATFE that are charged with enforcing the law. Finally, there are opinion letters which are issued by said agencies to try to help us mere mortals understand how they interpret the law according to… their opinion.

While we’re going to try our very best to point you in the right direction, it’s up to you to understand and obey the law. Just be aware that if you get in trouble, waving an opinion letter on the Supreme Court steps may not help you much if you get charged with a crime by someone with a different opinion. That’s my opinion, and I’m sticking to it.

What’s an SBR?

Before we get into this, it’s important to understand what an SBR is according to the definitions that the ATF uses, so let’s make a quick diversion on that topic. In the Code of Federal Regulations, Title 27: Alcohol, Tobacco Products and Firearms, Part 479—Machine Guns, Destructive Devices, and Certain Other Firearms, Subpart B—Definitions, §479.11 Meaning of terms, we find the following:

Firearm… (c) a rifle having a barrel or barrels of less than 16 inches in length; (d) a weapon made from a rifle if such weapon as modified has an overall length of less than 26 inches or a barrel or barrels of less than 16 inches in length;

More Definitions

Given that, you need to know what the law considers to be a rifle and pistol. From the same code, here ya go:

Rifle. A weapon designed or redesigned, made or remade, and intended to be fired from the shoulder and designed or redesigned and made or remade to use the energy of the explosive in a fixed cartridge to fire only a single projectile through a rifled bore for each single pull of the trigger, and shall include any such weapon which may be readily restored to fire a fixed cartridge.

Pistol. A weapon originally designed, made, and intended to fire a projectile (bullet) from one or more barrels when held in one hand, and having (a) a chamber(s) as an integral part(s) of, or permanently aligned with, the bore(s); and (b) a short stock designed to be gripped by one hand and at an angle to and extending below the line of the bore(s).

Boiling down all the legalese, the big deal between rifles and pistols is the stock. A stock on a pistol is “at an angle… below the line of the bore” and designed to be fired with one hand. A rifle is designed to be fired from the shoulder. This becomes important, so stay with me for a bit.

The SIG MCX Virtus SBR

What are your options to “create” an SBR?

So how can you get from zero to having an SBR? There are plenty of ways. I count three. Now that we’re all NFA law experts let’s take a look at each scenario.

Start with a rifle

If you buy a rifle and later want to convert it to an SBR, you can do that. If you refer back to the definition text, you’ll see that the law was written with this in mind. Originally it was created to discourage people from chopping stocks and barrels off rifles to make little baby rifles. You’ve always been able to do this legally; you just had to file the Form 1, pay $200, and not start any of the building processes until you get your tax stamp returned from the ATF. So, modifying a rifle into a short-barreled rifle has never been illegal, it’s just been regulated.

If you buy a rifle and want to convert it to a pistol, that’s also something that would require a tax stamp. Since pistols aren’t required to have tax stamps under the National Firearms Act, that doesn’t make much sense. It can become a modified rifle, or SBR, with a tax stamp. If you want to make a pistol per the legal definition, you’re better off just starting with a pistol rather than trying to convert a rifle into one.

Start with a pistol

You can convert a pistol to a short barrel rifle. Unless you live in one of the Republiks, pistols are not regulated. If you meet the legal qualifications for handgun ownership and can pass a NICS background check, you can get one. However, the minute you start the process of converting a pistol to a short barrel rifle, you wade right smack into the National Firearms Act and need to file paperwork and write checks. The process requires the ATF Form 1 submission, approval, and a $200 tax.

Perks of Starting with a Pistol

Starting with a pistol can be a great idea because the government is slow. Right now, it’s taking somewhere over 250 days for someone to process your Form 1 and cash your check. Maybe those artsy tax stamps are individually hand painted by Keebler elves? Whatever the reason, you’re going to have to wait a long time before you can convert your pistol into an SBR so you might as well get some use from it.

If you have a functional pistol, you can start acquiring the parts for your rifle, just don’t install any of them until you get your tax stamp. To be clear, there’s a potential gotcha here. It’s important to have the functioning pistol if you intend to start acquiring the parts for an SBR. If you have all the parts required for an SBR but don’t have parts to make a pistol, some ornery fed might assume that you have an unregistered SBR and that you just keep it disassembled. You won’t be able to prove that you’re using it as a pistol in the meantime if you don’t have any of the pistol parts on hand.

One more thing. If you start with a pistol, you can legally convert it to a rifle at any time you like with no paperwork or tax stamps. Pistols are legal, and rifles with 16-inch barrels and overall length of 26 inches are legal, so there’s no problem converting your pistol to a rifle.

Start with a receiver and parts

You can buy a lower receiver and make it into anything you want, provided you get the tax stamp first if you intend to build an SBR from the ground up. Don’t go off and buy all the SBR parts and stick them in a drawer until your tax stamp comes in. Just having all the gear to make an SBR before your application is approved can run you afoul of the law as we just discussed.

There’s one more thing to know regardless of which method you choose. You’ll need to have your receiver engraved with your name or the name of your trust and your city and state. Since you are “manufacturing” a firearm, you need to do like the big boys and stamp your identification.

Bag all the confusion and use a “fake” SBR

If you want something that has some rifle attributes but is smaller, and you don’t want to mess with any of the three scenarios we just discussed, you can just build or buy a rifle-caliber pistol. Unless you’ve been in a 24-hour news cycle induced coma the past couple of years, you’ve probably heard about pistol braces.

These devices were originally invented to help people shoot an AR-15 safely and effectively using one hand. Whether from amputation or injury, there are lots of folks who would want to do this, and the solution is pretty nifty. A pistol buffer tube has a rubber or plastic attachment that either wraps around the firing hand forearm or at a minimum, braces it, to help stabilize what is otherwise a heavy and unwieldy pistol.

Brace Yourself

Since you can rest just about anything against your shoulder, people quickly figured out that these braces make a reasonable substitute for a very short stock. Since the whole thing is a pistol, there’s no NFA process required. People who collect paychecks from the Treasury Department also figured this out and started to issue opinions on the matter.

First, they said, “No problem. As long as you don’t modify the pistol support from its original factory configuration, it’s not an SBR.” Later they said, “Hey wait a tic. If you hold this to your shoulder, you’ve modified the gun, and it’s now an SBR.” As of this writing, we’re in somewhat of a holding pattern. The ATF hasn’t sent anyone to jail for holding one of these to their shoulder, but it also seems like they’ve reserved the right to do so if they feel so inclined.

Whether you choose to use one of these pistol brace systems in a non-conventional way is up to you. There’s nothing with the word “law” behind it that’s clear on the matter, just a bunch of opinion letters, so you’re operating entirely at your own risk. User beware.

Here’s what I’m doing

I’ve got a C.O.P. integrated upper receiver and handguard from Aero Precision with a 7.5-inch barrel sitting on a shelf. While I might prefer a 10.5-inch barrel for 300 Blackout, it would be a shame not to give this one some tender loving care, right? So, the goal is to make this into a super-handy SBR, maybe even with a compact suppressor at some point.

I'm kinda eyeballing this Aero Precision M4E1 pistol lower. When I get my stamp, I'll just engrave the receiver, swap out the receiver extension tube, and add a real stock.

I’m kinda eyeballing this Aero Precision M4E1 pistol lower. When I get my stamp, I’ll just engrave the receiver, swap out the receiver extension tube, and add a real stock.

Tips for Building

Given all the legal mumbo-jumbo we’ve just been through, what’s the best way to approach this build project? My patience isn’t nearly as boundless as the ATF’s turnaround time to issue tax stamps. Can I wait over 6,000 hours before even starting to gather and assemble parts for a nifty 300 Blackout SBR? That’s an easy answer. No.

So, here’s what I am doing. I’m going to make a legal AR-15 pistol, chambered in 300 Blackout using the 7.5-inch Aero upper assembly. That step requires no federal permission slips other than passing the standard NICS background check when I buy the lower receiver.

Once I have the lower receiver and know the serial number, I’m going to file a Form 1 application to build an official SBR using that receiver. I can get it engraved with my information in any of the 6,000+ hours that I’ll be waiting on my shiny new tax stamp. By starting with a fully functional pistol, I’ll avoid any risk of having only parts on hand that can be used to build an SBR. Better yet, I’ll have a fully functional pistol to use while I wait for my permission slip.

On the downside, I’ll ultimately need to buy two receiver extension buffer tubes. The pistol tubes are different, and for legal reasons, I wouldn’t want a rifle tube on there anyway until the tax stamp comes back. When I have my stamp, I’ll be able to install a rifle tube at which point I’ll have an extra pistol tube. They’re not that expensive, so it’s no big loss. Maybe I’ll use it for a future project.

Now I wait. And wait. And wait.

{ 35 comments… add one }
  • R HolLand January 18, 2018, 4:52 pm

    It doesn’t matter what Federal Law or the U. S. Constitution says is you live in California. This state is just short of mass confiscation as already. The leaders have publicly said that the Constitution doesn’t apply here. If they violate it in passing a law, all that happens is the state gets sued by a person that can afford to do so and the state then spends mulitple millions of dollars fighting its own citizens in court. If the state loses, it just passed a new similar law and the process starts over again.

  • Jay January 16, 2018, 8:20 am

    Personally I don’t give a Rats behind what the ATF’s opinion is. They have and change opinions about as often as preachers have and change opinions about the bible. We The People of these United States need to take back our freedoms no if’s, and ‘s or but’s about it! We should Not even have to be reading about ways around archaic so called laws, we should be reading about how we have freedom, liberty and happiness without government interference! MAGA!

  • Scott Lawson January 15, 2018, 5:45 pm

    Brace can be shouldered only if brace is complete as designed (sb strap intact), lop is less than 13 1/2” and adjustment bolt is permanently locktited (kak blade).

  • bobh January 15, 2018, 11:20 am

    Personally, I see little utility in SBRs for non-military folks but if you want a SBR badly enough to spend the time, effort, and money to buy or build one AND you’re willing to pay the extra $200 for a tax stamp AND you’re willing to wait months for that stamp AND you’re willing to accept that your barrel will limit the performance of your selected caliber (in many cases it will limit it rather severely) go right ahead. Just please don’t discharge your rifle caliber SBR near me. My hearing loss is bad enough already.

    • kyle January 15, 2018, 7:54 pm

      Though I don’t waste my money on SBR tax stamps, I have built a few “pistols” with braces. I can tell you that for non-military applications it is what I prefer because I can use my suppressor with it and not have a stupidly long weapon. I’m not sure what you consider severely limited performance, but my 12.5″ 308 can spit out a 150gr interlock at 2500 fps, and a 130gr barnes TTSX at 2700 fps. It’s my primary deer and pig gun because it’s so handy and easy on my ears. My 5.56 coyote gun has a 11.5″ barrel and I use a can with it. It get’s a lot of use as well for the same reasons.

    • ejharb January 17, 2018, 6:12 pm

      Or put another way,,,
      I don’t have want or foresee a reason for people to have a short handy carbine so I’m all in favor of you either having to go thru red tape pay the cost of 2 family dinners at a nice restaurant and wait 1/70th of a avarice human lifetime to get one.or I’ll gleefully clap as the government burns your house down after trapping your family in it or blows your wife’s head off as she breastfeeds your baby. You sir are a greater enemy than sen sumer and Feinstein combined.

      • left coast chuck January 18, 2018, 6:42 pm

        And you, sir, are not free to express opinions that run contrary to what I firmly believe.
        “What’s that?” you say. “What about my First Amendment rights to free speech?”

        Well, sir, you are enthusiastically willing to negate my rights under the Second Amendment, I believe that gives me the right to negate your rights under the First Amendment. After all, if we start chipping away at rights who is to say where we stop?

        I don’t feel the need to go to all the trouble to make an SBR but that doesn’t mean Mr. McHale, if he so chooses cannot make one. It is protected under the Second Amendment. The Constitution still contains provisions for issuance of Letters of Marque. A letter of marque presupposes that you are going to wage naval warfare against declared enemies of the United States. If you are going to wage naval warfare against declared enemies of the United States, you had better be prepared to have some serious weaponry beyond an SBR.

        When I was a boy, the father of a friend of mine owned a very nice large yacht. Actually, I think it belonged to the Philly Mafia boss, but it was in my friend’s father’s name. In order to suppress German submarines along the eastern seacoast, his very nice large yacht was equipped with two twin .50 caliber machine guns and he had depth charge racks on the stern to hold four depth charges and they stored more topside on the deck. He patrolled the Delaware River and the Chesapeake Bay and a few miles offshore in his armed yacht. While my friend’s father was not issued a formal letter of marque, he certainly possessed a de facto letter and was empowered to attack German shipping that he encountered. Folks don’t remember the early days of WWII anymore, but like so frequently, we were caught with our trousers down and our shoes untied. Where we lived we could see light in the sky at night from the ships being sunk by U-boats. The Brits, after WWI, confiscated weapons because they were afraid the unions might start trouble. When WWII came along they had to beg rifles from the civilians in the United States. Without the civilian market, there would be no weapons companies turning out small arms for the U.S. Armed Forces. We would be forced to buy them from foreign countries.

  • KCsmith January 15, 2018, 11:04 am

    Braces are not in any “holding pattern”. There have been three statements by the ATF regarding braces. You’ve listed the first two. That second ATF opinion is now about three years old, as it was released in January 2015.
    The ATF revised their 2nd statement many months ago, in early 2017, stating that shouldering an unmodified brace does not constitute a redesign.
    I’m surprised you wrote this article and did not know this information. Not well researched obviously, and ruins any kind of credibility the article may have had.

    From April, 2017
    The new clarification of opinion letter states, “an NFA firearm has not necessarily been made when the device is not reconfigured for use as a shoulder stock – even if the attached firearm happens to be fired from the shoulder.”

    • Tom January 15, 2018, 12:05 pm

      It’s definitely a holding pattern and I’m aware of the other opinion. That’s exactly the issue. Opinions aren’t legally binding and subject to change at any time and in any direction, as the article says.

      • KCsmith January 15, 2018, 1:13 pm

        Yet you decided not to bring up that 3rd ATF opinion, which you were aware of, in this article, but did address the first two opinions. Interesting choice.

        So, to sum this up, the ATF releases an opinion that shouldering a gun attached to a non-modified brace does not qualify it as an NFA weapon, and that’s not clear enough for you? The ATFs statement isn’t legally binding, so you think that they might arrest you for something which they clearly stated was perfectly legal?

        I disagree. That doesn’t seem like a holding pattern to me at all. And I can’t imagine how it does to you, to be honest.

        • Tom McHale January 15, 2018, 1:54 pm

          I may just be more cautious on the issue than you, and that’s OK. Here’s why I consider it an open issue.

          An open letter (often called and opinion letter) is not in any way, shape or form a law. It cannot make or define law. An opinion letter does not make something “perfectly legal.” It also can’t make something illegal. The contents of those letters are not anywhere in the US Code. It’s just an answer, usually to a specific question. The next question that comes in may get a similar opinion or a totally different one, even in the opposite direction, which is what happened – twice – on this particular topic. The next ATF boss who writes an opinion letter may support the previous opinion or some up with a totally new one. Until it’s tested in a courtroom and becomes part of case law, it remains an opinion. You can’t wave opinion letters on the Supreme Court steps to get out of jail free.

          This whole thing is exactly the type of ambiguity that needs to be resolved in a courtroom because an opinion letter is just what it says. An opinion on a question.

          Is the ATF gonna start sending people to jail for holding pistol-brace ARs too high? I seriously doubt it, at least under the current administration.

          Is the ATF gonna campaign to clarify actual law (not opinion) that these braces are perfectly legal to fire from the shoulder? I seriously doubt that too.

          Is trashing this whole ridiculous SBR and silencer law the real solution? Yep. Pester your Congress Critters.

  • Gregory Romeu January 15, 2018, 9:49 am

    “Those willing to sacrifice a little part of liberty for safety, deserve neither.”

    Seems to me, more Americans need to grow bigger balls and UNREGULATE their complacent asses BACKWARDS to The Constitution, which CANNOT be wordsmithed into the state of complacency in which you cower in!

    • ejharb January 17, 2018, 6:15 pm

      Here here! Please for the sake of future freedom be fruitful and multiply. If I had a couple supermodels to spare I’d introduce them to you

  • KenW January 15, 2018, 9:36 am

    They regulate it now ??
    What about the old TC Contenders with a 14″ barrel and a shoulder stock ?
    I shot a 14″ 44mag and a 30/30 with the shoulder stock just as they were sold back in the 80s.

    • Tom McHale January 15, 2018, 12:25 pm

      If I remember correctly, it was about a 20-year lawsuit to finally resolve that one:-) I’ll have to look up the beginning and final resolution dates, but I think it took forever…

  • Roger January 15, 2018, 9:09 am

    250 days for a tax stamp. Who do you know?

    • KCsmith January 15, 2018, 11:09 am

      My last form 1 suppressor stamp took over 15 months, about 460 days. Late July 2016 to early November 2017.

  • mac10tom January 15, 2018, 7:31 am

    My project was an MPX. Bought a pistol. Submitted form 1 with all the original SIG markings as the serial #.and manufacturer. Approved as submitted. NO ENGRAVING.

    • LPD256 January 15, 2018, 12:53 pm

      mac10tom-I did the same with an MPX. When I got my tax stamp and added my stock, I was informed I just became the “manufacturer” and had to engrave the name of my trust on the receiver to make it legal. I’m no expert, but I trust the dealer that told me. I bought a second stamp as I added a suppressor. Throw in a Romeo 4 sight and a Geisslle trigger and it is an awesome but expensive adventure. Do yourself a favor and see what the NFA says about procedures involved in taking your SBR to a different state. I just bought a Sig PM400 pistol with a SigBrace. Less hassle for sure if one wants to stay legal.

    • allblues January 15, 2018, 2:54 pm

      mac10tom-I also have a form 1 MPX, in addition to 3 other form 1 SBRs. I suggest that you check ATF regulations for engraving requirements, as they are very specific as to size, depth, location and who or what must be engraved. As the holder of an approved form 1 stamp you are considered the manufacturer, and your name or the name of your trust, city and state must be engraved. If you have a “multi caliber” lower you must also engrave the caliber.

  • Blue Dog January 14, 2018, 1:51 pm

    This is why I keep mentioning pistol braces in conversations with bump stocks! If the ATF is going to reconsider bump stocks, these pistol arm braces need to be in that same conversation. Thank you to the author, Tom McHale, for openly acknowledging that these braces are being used exactly this way out there, to shoulder what would otherwise be pistols!

    • Mike V. January 15, 2018, 7:38 am

      Like bump stocks, ATF has already looked at this plenty of times.
      They already consider a brace a stock if that’s what you intend it to be.

      But why not, a federal agency

    • Rich W. January 15, 2018, 8:11 am

      No, braces should not be in that discussion because the discussion should not be happening at all. The ATF just needs to leave well enough alone for once. We have the approval for the braces and the bump stocks and, just because some politician or Fudd gets their panties in a bunch, there is no reason to change it. A true supporter of the 2nd Amendment would understand this.

    • kyle January 15, 2018, 8:16 am

      Blue Dog, as always you show how much of a moron you are in your comments. The only thing braces help a shooter with is to save him/her some money and still be legal. It’s still just a regular gun whether it has a stock or brace. Putting braces in the same category as bump-stocks makes no sense at all. If somebody wanted to use an SBR to carry out a murder they could just build one illegally. I guess you forgot that criminals don’t obey laws. Big surprise coming from a “Blue” dog.

    • Robert January 15, 2018, 9:58 am

      I guess you missed the “shall not be infringed “ of the 2nd Amendment. Time for you to go read it

      • Blue Dog January 16, 2018, 12:06 pm

        Oh no, I saw it. It comes shortly after “well-regulated militia”. As in, the right is reserved to a group that is operated by state governments [not individuals] that are acknowledged at the front end where the federal government giving the individual states this right that these militias will be subjected to regulations.

        • Tom McHale January 16, 2018, 3:20 pm

          This ^^^ made my day by being the most entertaining understanding of the term “well-regulated militia” that I have ever seen. A 30-second look at the founding documents, letters, and notes written by the guys who wrote the Second Amendment will show how utterly ridiculous this definition is. I mean this literally – 30 seconds.

          • ejharb January 17, 2018, 6:21 pm

            Yeah I coulda swore it said THE RIGHT OF THE PEOPLE instead of THE RIGHT OF THE MILITIA. Wadda ya know?

          • TJ January 18, 2018, 7:48 am

            By his logic the Militia only has a right to free speech…….

        • Dan January 18, 2018, 9:55 am

          Yup, Blue Dog truly is an example of the evil that us good folks will always have to fight. There will always be those looking to stomp personal liberty and slowly hand every one of our rights over to big government. It’s actually good that scum like him post here. As we sometimes find petty reasons to argue amongst ourselves, he reminds us who the real enemy is.

    • Tom January 15, 2018, 10:30 am

      “Openly acknowledging?” Seriously? Like it’s some sort of confession?

      I could care less about how someone chooses to hold their firearm. I don’t think it’s Uncle Sam’s business either. Want to strap it to your arm? Great, have fun! Want to hold it to your shoulder? Fantastic, hope you score all X-rings! Want to balance it on your nose? I’ll be super impressed after you stop bleeding!

    • Chuck Matson January 15, 2018, 11:10 am

      Blue Duck doesn’t understand the second amendment, so maybe he or it should just go back to huffpo where he or it will be happy.

      • ILL WILL January 15, 2018, 12:49 pm

        You forgot Heshe, shehe, zeher, zehe, zegay, gayze!!!! Who knows, Blue Dog may be a bot and we have to start respecting those opinions too!!! Don’t you just love “progress”

    • Charlton January 15, 2018, 11:39 am

      Blue dog should you not be in someone’s lap

      • ejharb January 17, 2018, 6:24 pm

        Blue (dog)lives matter.
        Unless they’re killing your chickens or chasing your cows.or otherwise”infringing”

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