NFA and Prison: Design Mistakes That Can Get You Locked Up
DISCLAIMER: We do not offer legal advice and nothing contained herein should be interpreted as legal advice. The legality of possession of any firearm is dependent on you and the state in which you reside. You are responsible for you, so understand the law before you venture into unfamiliar waters.
Introduction
If you’re building or modifying an AR-platform firearm, you may be just one misstep away from federal prison. That’s not hyperbole. The National Firearms Act (NFA) governs specific firearm configurations, and violating it—even accidentally—can lead to a felony conviction, a $250,000 fine, and up to 10 years behind bars. This article explains what the NFA covers, how builders commonly break the law, and what you can do to stay compliant.
This image from @Rational.Rebel pretty much sums up the logic and clarity of the NFA:
What Is the National Firearms Act?
Passed in 1934, the National Firearms Act was the first major federal gun control law in the U.S. It was designed to regulate and restrict ownership of firearms deemed particularly dangerous or concealable. Today, it still applies to certain categories of firearms that require special registration and taxation.
The Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) enforces the NFA.
Types of Regulated Firearms
Federal law divides firearms into two main categories:
Title I Firearms
These are the most common firearms owned by civilians and are regulated under the Gun Control Act of 1968. They include:
- Pistols and Revolvers: Handguns designed to be fired with one hand.
- Rifles: Shoulder-fired firearms with a barrel length of 16 inches or more (including any permanently-attached muzzle device) and an overall length of at least 26 inches.
- Shotguns: Shoulder-fired firearms with a smooth-bore barrel length of 18 inches or more and an overall length of at least 26 inches.
Title II Firearms
These are regulated under the NFA and require registration with the ATF, a tax stamp, and additional legal steps. These include:
- Machine Guns: Any firearm that fires more than one round per trigger pull, or parts intended for such use (including drop-in auto sears). For the average citizen, a machine gun must be transferable, per federal definitions. You may not manufacture a machine gun, unless you are a Type 07 FFL and are registered as Class 2 SOT, and even then, you may only manufacture machine guns for government agency sales. We will not discuss machine guns further in this article.
- Short-Barreled Rifles: A rifle with a barrel shorter than 16″ (including any permanently-attached muzzle device) or an overall length under 26″.
- Short-Barreled Shotguns: A shotgun with a barrel under 18″ or overall length under 26″.
- Suppressors: Any device designed to muffle a firearm’s report. Suppressors may be purchased as suppressors, or may be manufactured from a variety of readily available components. While we believe that a sound suppressor is a great accessory for the AR, it is not part of the firearm, itself. As such, we will not discuss sound suppressors further in this article.
- Destructive devices: Explosives, grenades, and large-bore firearms (over .50 caliber) not intended for sporting use. None of these pertain to the construction of an AR, so we will not discuss these further in this article.
- Any Other Weapons (AOWs): Concealable, non-standard firearms like disguised guns or pistols with vertical foregrips. “Any Other Weapon” is basically a junk drawer classification for any firearm or associated device that cannot be classified as a Title I firearm and does not fit into any other category of Title II items.
The Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) enforces the NFA. While Title I firearms are what most gun owners think of as “standard,” even these can become Title II firearms with the wrong configuration.
Transfer and Ownership of Regulated Firearms
Title I firearms (rifles, shotguns, pistols/handguns) are readily transferrable with relative ease. Generally, they may be manufactured by anyone otherwise permitted to posses a firearm for personal use without any registration or background check, or they may be purchased with a simple background check. Note that if you are not a Type 07 FFL, you MAY NOT manufacture a firearm with the intent to sell it.
Manufacture, purchase, or possession of Title II firearms and devices (machine guns, short barreled rifles/shotguns, sound suppressors, destructive devices, and any other weapon) is less straightforward. These devices require additional notification, registration, and permitting at the federal and local levels.
Legal Consequences of Violating the NFA
Violating the NFA carries steep penalties:
- Up to 10 years in federal prison
- Up to $250,000 in fines
- Forfeiture of your firearms
- Permanent loss of gun rights
Even if your actions were unintentional, ignorance is not a defense. The ATF has prosecuted individuals for technical infractions.
What Features Will Get Me In Trouble?
The following components and features must be considered very carefully:
- Barrel: If you install a barrel under 16″ (as measured from the bolt face to the muzzle or end of any permanently-installed muzzle device), you have a pistol and half the recipe for a Short-Barreled Rifle (SBR).
- Buttstock: If you install a buttstock on a pistol (barrel less than 16″), you have a Short-Barreled Rifle (SBR).
- Foregrip: Any grip installed in front of the pistol grip can be a problem. If you install a vertical foregrip (VFG) on a pistol (barrel under 16″), you have an Any Other Weapon (AOW).
- Lower Receiver: If you have a lower receiver in your possession that is drilled for an auto sear pin, you can be found guilty of intent to assemble a machine gun.
- Trigger: If you have in your possession a select fire trigger group (burst or auto), you can be found guilty of intent to assemble a machine gun.
- Full-Auto Conversion Devices: If you are in possession of an auto sear, drop-in auto sear (DIAS), lightning link, or other device that effectively converts the gun to full-auto, you can be found guilty of intent to assemble a machine gun.
- Disconnector: If you “accidentally” omit the disconnector, your gun will be full-auto (sometimes called “runaway trigger”, “slap fire”, “slam fire”, “kitchen table machine gun”, or “open loop fire control”). Regardless of whether it is done intentionally, you can be found guilty of illegal conversion to and possession of a machine gun.
- Pistol Brace: The wind seems to shift back and forth on pistol braces. Currently, a consumer can install a pistol brace on a pistol and it is not technically a Title II SBR. However, remember the definitions of “pistol” and “rifle”: if you shoulder the weapon, it is a rifle and the ATF is still granted authority to enforce their will on a case-by-case basis.
NFA Considerations for the AR
Default Classification by Lengths
| OAL less than 26" | OAL at least 26" | |
| Barrel Length less than 16" | Pistol | Pistol |
| Barrel Length at least 16" | Pistol | Rifle |
Overall Length (OAL)
Overall length is measured from the rear of the buttstock (or receiver extension, if a pistol) to the tip of the barrel with any removable muzzle device removed. If the firearm is equipped with an adjustable buttstock, the measurement is taken with the buttstock fully extended. If a muzzle device is permanently attached (i.e. pinned and welded), the measurement is made to the tip of the muzzle device.
Barrel Length
If an ATF agent shows up at the range and you are out there with a firearm that is questionable, they will measure the length of your barrel very simply: by running a rod down the bore of the barrel and measuring the distance between the bolt face and the farthest fixed point of the barrel.
If you want to see how your firearm measures up, get yourself a long rod that will fit down the bore of your firearm. You can use a cleaning rod or go to Lowe’s or Home Depot and buy a 0.1875″ (for 5.56) or 0.25″ (for 7.62) wooden dowel.
- With the bolt closed, run a rod/dowel down the bore of the barrel as far as it will go. It should be touching the face of the closed bolt.
- With the rod fully inserted, mark it where it emerges from the crown of the barrel. It is best to remove any removable muzzle device for this. If you have a permanently attached muzzle device, you can mark where the rod/dowel exits the muzzle device, as this is the legal “end” of your barrel.
- Measure the rod/dowel from the end that was touching the bolt face to the mark you just made.
Reclassification of Pistols Based On Attachments
| Attachments | Pistol | Rifle |
|---|---|---|
| None | Pistol (Title I) | Pistol (Title I) |
| Buttstock | SBR (Title II) | Rifle (Title I) |
| Pistol Brace | Pistol (Title I)* | Rifle (Title I) |
| Vertical Foregrip | AOW (Title II) | Rifle (Title I) |
| Angled Foregrip | Pistol (Title I) | Rifle (Title I) |
| Hand Stop | Pistol (Title I) | Rifle (Title I) |
| Finger Stop | Pistol (Title I) | Rifle (Title I) |
| Barricade Stop | Pistol (Title I) | Rifle (Title I) |
Buttstocks
This one is relatively simple.
Pistol Upper + Buttstock = SBR
If you put a buttstock on a pistol, it is no longer designed to be fired with one hand. Therefore, is no longer a pistol. If a firearm 1) has a rifled barrel, 2) does not meet qualify as a rifle by both OAL and barrel length, and 3) is outfitted with a buttstock, the NFA classifies it as a short-barreled rifle (a Title II weapon).
Pistol Braces
This one is a little less simple.
A pistol brace is a device that can be installed on a pistol (especially an AR-style pistol) to allow a shooter to more easily wield a heavy weapon with one hand. This device was designed to allow disabled shooters, who would not otherwise be able, to handle an AR (or similar) pistol.
While some pistol braces look very similar to buttstocks, and it is very natural to shoulder a pistol outfitted with a pistol brace, the ATF generally accepted the use of this accessory for a long time.
In 2022, the ATF set policy in motion that would render any pistol brace installed on a pistol a short-barreled rifle and, if not registered as an NFA Title II firearm, illegal. In 2023, this ruling went into law.
After a public shitstorm-fueled Supreme Court ruling, the ATF has clarified that, since they do not regulate firearms accessories, the classification of a pistol equipped with a stabilizing brace as an NFA Title II firearm only applies if the pistol brace is installed by the firearm manufacturer.
For the time-being, if you install a pistol brace on an AR pistol, you are not breaking the law.
Vertical Foregrips, Angled Foregrips, Hand Stops, Finger Stops, and Barricade Stops
So far, things seem somewhat straightforward. The waters get muddy from here on out.
Pistol Upper + VFG = AOW
If you own an AR pistol, you MAY NOT affix a vertical foregrip (VFG) to the area forward of the pistol grip, without first registering the AR as an AOW. Pistols are defined as being designed to fire with one hand (even if you routinely use two). When you put a VFG on it, it magically transforms into a pistol designed to fire with two hands. Any. Other. Weapon.
Pistol Upper + AFG or Hand Stop or Finger Stop or Barricade Stop ≠ AOW
But don’t confuse a vertical foregrip for any other device attached to the fore-end of your pistol.
An angled foregrip (AFG) is one that is installed forward of the pistol grip. But doesn’t protrude straight down like a VFG. One would think that this wouldn’t matter, given the definition of a pistol and the transformation that occurs with a VFG. However, the ATF has determined that AFGs are not vertical foregrips, and therefore, do not convert a pistol into an AOW.
Hand stops and finger stops are designed to keep your hand from accidentally slipping off of the handguard and into the path of a bullet. Now, these are vertical protrusions from the fore-end of your pistol…but they aren’t long enough to be considered foregrips. Therefore, installing a hand stop or finger stop does not convert a pistol into an AOW.
Barricade stops are vicious toothed creatures that are designed to jam into wooden barricades for additional support. You probably wouldn’t want to wrap your fingers around one of these. But even if you did, its not considered a VFG, so it does not convert your pistol into an AOW.
We know this is confusing and doesn’t quite follow sound logic. We are not arguing with this week’s opinion (which excludes AFGs, hand stops, finger stops, and barricade stops from the Title II features list), but you should be aware that opinions can and do change. Most of the time, opinions change because of gun owner behavior…so be responsible. Thankfully, if the ATF reverses its opinion on AFGs, hand stops, finger stops, and/or barricade stops, they are easy enough to remove and cheap enough that it probably won’t ruin your life.
Think You’re Safe Because the Parts Aren’t Assembled?
Think again. Under federal law, you can be charged with possessing an unregistered NFA item even if it’s still in pieces. It’s called constructive possession, and it’s one of the most common—and least understood—ways builders get in trouble with the ATF.
NFA: How to Stay Legal
If you are building an AR, you have a few options:
- Treat the parts as a whole. Just because it’s not assembled, doesn’t mean you aren’t breaking the law. PLEASE read our article on Constructive Possession…your freedom as a DIY-er depends on a clear understanding of this concept and compliance with the nuance that will be used against you.
- Install a barrel that is nominally at least 16″ long. It isn’t a bad idea to confirm that the barrel length measures at least 16″ per the procedure above.
- If you want to minimize the length of your AR rifle, you can install a shorter barrel if you 1) permanently attach the muzzle device (pin and weld), and 2) the combined installed length of the barrel and muzzle device meet the minimum 16″ requirement (be sure to factor the overlap of threads).
- If you intend to build an AR with a barrel that is less than 16″ (including any permanently-attached muzzle device), you can build it as a pistol without any further federal consideration (be aware of state and local laws).
- If your AR has a barrel under 16″ (including any permanently-attached muzzle device), DO NOT PUT A BUTTSTOCK ON IT, at least until you register it as an NFA SBR.
- If your AR is built as a pistol (i.e. no buttstock + barrel under 16″), DO NOT PUT A VERTICAL FOREGRIP ON IT, at least until you register it as an NFA AOW.
Additional Resources: Navigating NFA Compliance
To deepen your understanding of the National Firearms Act (NFA) and ensure compliance, consider exploring the following official resources:
- ATF National Firearms Act Overview – Comprehensive information on the NFA, including its history and regulatory scope.
- ATF Firearms Forms – Access to all necessary forms for NFA applications and registrations.
- ATF eForms System – Submit NFA forms electronically for faster processing.
- ATF Firearms Q&A – Answers to common questions about firearms regulations and procedures.
- ATF National Firearms Act Division – Information about the ATF’s NFA processing branch.
By leveraging these resources, you can ensure that your firearm activities remain within legal boundaries and that you’re well-informed about your rights and responsibilities under the NFA.
Final Thoughts: Navigating the NFA—Stay Informed, Stay Legal
Building or modifying an AR-platform firearm offers enthusiasts a rewarding experience, but it’s crucial to recognize the legal boundaries set by the National Firearms Act (NFA). Unintentional missteps, such as creating a short-barreled rifle (SBR) without proper registration, can lead to severe federal penalties, including fines up to $250,000 and imprisonment for up to 10 years.
To ensure compliance:
- Understand Firearm Classifications: Differentiate between Title I and Title II firearms. Title II includes machine guns, SBRs, short-barreled shotguns, suppressors, and “Any Other Weapons” (AOWs), all of which require strict adherence to NFA regulations.
- Stay Updated on Laws: Firearm laws can vary by state and are subject to change. Regularly consult official resources or legal counsel to stay informed about current regulations.
- Seek Expert Guidance: When in doubt, consult with professionals or legal experts specializing in firearm laws to ensure your modifications or builds are compliant.
At Para Bellum Arms, we emphasize the importance of responsible firearm ownership and adherence to all applicable laws. By staying informed and cautious, you can enjoy your firearm projects while ensuring they remain within legal parameters…and you remain free.
Frequently Asked Questions
Do I need a tax stamp for an AR-15 build?
Only if you are building an NFA item such as:
- A short-barreled rifle (SBR),
- An AOW, or
- A suppressor.
Standard rifles and pistols don’t require a tax stamp. Filing Form 1 and receiving ATF approval is mandatory before modifying or assembling NFA-regulated builds.
Is my AR-15 an SBR under the NFA?
Your AR-15 is classified as a short-barreled rifle (SBR) if it has a barrel length under 16 inches and is equipped with a stock or is intended to be fired from the shoulder.
SBR laws define these configurations as regulated firearms under the National Firearms Act, requiring ATF registration and a $200 tax stamp before possession or assembly is legal.
Can you go to jail for an unregistered SBR?
Yes. Possessing an unregistered SBR is a felony under federal law, punishable by up to 10 years in prison and a $250,000 fine. Always file a Form 1 and receive your tax stamp before assembling or possessing an SBR configuration.
How can I legally avoid creating an SBR?
To stay compliant, either:
- Use a barrel that is 16 inches or longer with a rifle stock, or
- Use a pistol brace or no stock with a barrel under 16 inches on a pistol lower.
Avoid mixing short barrels and rifle stocks unless you’ve filed a Form 1 and received ATF approval.
Can I use a rifle stock on a pistol lower?
No. Installing a rifle stock on a pistol lower with a barrel under 16 inches creates an SBR, which is illegal without ATF approval and a tax stamp. This is one of the most common (and costly) mistakes builders make.
What are the NFA rules for AR-15 pistols and rifles?
Under the NFA:
- Rifles must have ≥16″ barrels and be ≥26″ overall.
- Pistols can have barrels of any length but must not have stocks.
- SBRs require a tax stamp if under 16″ with a stock.
Each configuration changes the firearm’s legal classification, so builds must match their intended category.
How do I build a compliant AR-15 pistol?
AR-15 pistols are legal if configured correctly, but easily become illegal under the NFA.
To remain legal:
- Use a pistol-marked lower.
- Do not install a stock—use a buffer tube or brace.
- Avoid vertical foregrips unless the overall length is ≥26″. For now, angled foregrips (AFGs), hand stops, finger stops, and barricade stops do not render a pistol an AOW.
Stick to handgun-style configurations unless you’ve filed Form 1 paperwork.
What’s the difference between Title I and Title II firearms?
- Title I: Standard rifles, shotguns, and handguns (regulated under the Gun Control Act).
- Title II: NFA-regulated items like machine guns, SBRs, suppressors, and AOWs.
AR-15s can fall under either depending on configuration. For example, an SBR is a Title II item, while a full-length rifle is Title I.
What is constructive possession under the NFA?
Constructive possession means you could be considered in possession of an unregistered NFA item if you own all of the components to assemble an NFA item—even if you don’t assemble it.
For example, you can be found guilty of constructive possession by simply having the following stored next to one another (even if not assembled together):
- A short barrel upper and
- A rifle lower with a stock
Constructive possession is a tricky trap. Refer to our article on Constructive Possession for more information.
What makes a weapon an AOW under the NFA?
An “Any Other Weapon” (AOW) is a catch-all category that includes:
- Smoothbore pistols
- Pistol grips-only shotguns under 26″
- Certain disguised firearms
- Pistols with a vertical foregrip in front of the pistol grip
In general, the last bullet is the only one relevant to the AR-15.
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