Form 1 FAQ

MachIVshooter

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Wanted to compile something that can perhaps be stickied to help guys with form 1, or "build it yourself" questions.

Q: What is "form 1"?
A: "Form 1" is an application to make and register an NFA firearm; short barreled rifle, short barreled shotgun (SBS), Any Other Weapon (AOW), Destructive Device (DD) or Firearm Silencer (Suppressor).

Q: Who can make a Form 1 NFA firearm?
A: Anyone who can legally possess an NFA firearm in their state of residence can manufacture one with an approved Form 1

Q: Do you have to have an approved form 1 before manufacturing the NFA firearm?
A: Yes. Unlike a licensed manufacturer, who has to manufacture first and then file a Form 2 to register, a Form 1 builder must have an approved form 1 in their possession before manufacturing.

Q:
Do I have to build it myself, or can I contract the work
A: Manufacture of NFA firearms is about as convoluted as NFA itself. For this question, we'll break it down by NFA Weapon type

-SBR, SBS: You can shorten the barrel or install shortened barrels yourself. Anyone can help you as long as you're present for the entire duration of service. To drop the weapon off or ship it for barrel shortening or installation of short barrels, it must go to a licensed manufacturer, which is a type 07 or type 10 FFL with class II SOT, henceforth referred to as 07/02 or 10/02. While it is a gunsmithing service, ATF considers these "substantial" modifications to be manufacturing, so, while the manufacturer doesn't need to engrave their info on a form 1 NFA item, they do have to be properly licensed to perform the service and to possess NFA firearms.

-Silencer: There are certain steps that must be done by the Form 1 builder or under their direct supervision. While you can buy a lot of "solvent trap" parts, the front cap and baffles must be made, whether from scratch or by drilling a hole, by the registered builder or under their direct supervision. You cannot send your parts out to be completed by anyone else, not even an SOT. Once the silencer is completed, however, an 07/02 or 10/02 can perform any service on it up to and including replacing every part but the tube.

-AOW:
AOW is a little more complex because of the definition of AOW, which can range anywhere from a handgun with smooth bore to a cell phone or cane gun, and tons of things in between that aren't title I firearms and also do not fit other NFA definitions. Basically, if you're turning an existing firearm into an AOW, it works the same as SBR/SBS. If it is to be built entirely from scratch or parts, now it's manufacturing, not gunsmithing, and needs to be completed by the F1 builder or under their direct supervision.

-Destructive device:
Destructive devices are not an area I have much expertise in, but my understanding of the regulations are that it would have to be built by or under direct supervision of the Form 1 builder. Service of a DD must be performed by the registered builder/owner or a type 10/02 SOT. A type 10/02 cannot manufacture a DD that's Form 1 registered, but can make alterations to an existing serialized firearm that will render it a DD.

-Machine Guns: Sorry, there is no provision for a Form 1 machine gun. That got nixed in May of 1986 with the Hughes amendment to Volker/McClure (FOPA). The only way to own a machine gun is Form 4 transfer and many thousands of dollars. Even us SOTs don't actually "own" the post sample machine guns; our companies do, and we have to transfer or destroy them if we ever stop paying SOT or give up our license.

Q: Can I make changes to my Form 1 firearm?
A: Yes for some, no for others. SBRs or SBSs can have barrel length and caliber altered, though you need to either retain the ability to configure it as listed on the Form 1, or send a letter to NFA branch permanently amending form 1. AOWs can be altered in some ways similar to SBR/SBS, but you should inquire with ATF before making changes, since AOW is not a well-defined category. DDs can have length configuration changed, but not caliber AFAIK. Silencers are a done deal once completed, and can only be repaired by an 07/02 or 10/02. Silencers also cannot have their length or caliber changed by anyone, ever, except minimal shortening for repair purposes. About the only thing a Form 1 builder can change on a silencer is the mount, or the front cap with certain limitations. An 07/02 or 10/02, however, can repair or replace any part of a Form 1 Silencer except the serialized tube.

Q: Can I have spare parts for my NFA firearm?
A: The short answer is yes, except for silencers. Other than the serialized receiver, all other parts are just that-parts. However, you do need to consider constructive possession possibilities, and it would be unwise to keep enough parts around to build another NFA firearm. With silencers, spare parts are a no-go. Different mounts are OK, as those are just mounts. But you cannot have any extra internal parts, period. Under the law, silencer parts are silencers in and of themselves, so having just one extra baffle lying around would be possession of an unregistered silencer.

Q: If I break my Form 1 firearm, can I build another with the same engraving?
A: No. Unlike title I firearms, which can be replaced by the manufacturer with the same or another serial number, if the serialized part of an NFA firearm becomes irreparably damaged, you will have to file another form 1 to make & register a new firearm. You also need to send ATF a letter detailing that your NFA firearm has been destroyed so that it can be struck from the registry.

Q: Can I transfer a Form 1 firearm?
A: Yes, they transfer on a Form 4, just like any other NFA firearm

Q:
Who can possess my Form 1 firearm
A: Only you or, if done on a trust, other trustees. An SOT may possess for repair/resale/transfer purposes, and LE or government agents acting in an official capacity. Anyone who is not prohibited from possessing a firearm may use your NFA firearm, but only under the direct supervision of the registered individual owner or trustees. And no, you cannot loan your Form 1 firearm to your "cop buddy"; LEO possession of NFA firearms not registered to them has to be official, either department owned firearms or one surrendered/taken into custody/evidence officially. Being an LEO doesn't exempt them as individuals from the provisions of NFA or GCA.

Q: Do I need to carry paperwork for my Form 1 Firearm?
A: Yes, or at least a digital image of your approved Form 1. While only ATF agents can demand to see documentation, any LE or federal agent can ask, and if you choose not to show, they can certainly detain you until an ATF agent arrives if they have reason to believe you are not legal to possess the weapon.

Q: Can I "de-register" an NFA firearm
A: Basically, yes. A Machine Gun or Silencer can be destroyed and removed from the registry. An SBR, SBS, DD or AOW can be either destroyed or permanently reconfigured into a title I firearm and struck from the registry. For example, replacing the short barrel on a rifle with a 16" tube, or taking a 20mm caliber barrel off of your DD and replacing with an Anzio 20/50 barrel or .50 Fat Mac barrel, renders them title I firearms. An NFA firearm that has been permanently reconfigured into a title I firearm can be possessed, conveyed and transferred as a title I firearm. If you do permanently reconfigure, you need to send a letter detailing that as with a destroyed firearm, or it will remain on the registry and could potentially cause problems for you later if the new owner makes an illegal NFA firearm out of it, as ATF could very well think that you transferred the NFA firearm illegally.

*Temporary title I reconfiguring of registered NFA firearms can be done for the purpose of traveling interstate without a form 5320.20

Hope this is helpful, I'll edit & update as I think of other Q/A or if I become aware of any changes in legislation or ATF policies.
 
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Always good to help others. The third sticky in this section is actually a pretty in depth FAQ with form 1's, 4's, etc. Might be worth reading through it and giving the author feedback on anything that's changed in the last couple of years.
 
The third sticky in this section is actually a pretty in depth FAQ with form 1's, 4's, etc.

I though it might be helpful for the F1 crowd to have an FAQ with more answers specifically about F1 (especially silencers), since the very short wait times now are inspiring more people to go that route (or so it seems). I know there are forums dedicated to form 1 stuff, but I'm not on any of those, and I expect a fair number of our members here aren't either, since they're mostly a lot of monotonous chatter about AR SBRs and "solvent trap" parts.
 
On SBR conversions that only become an SBR by changing the Stock and not the barrel itself. Such as making a Mares Leg into a SBR by simply replacing the stock with that of a rifle stock.

1. Does the rifle still need to be engraved, and if so where does the firearm need to be engraved?

2. Are we allowed to remove the rifle stock and replace the original stock to turn it back into a handgun, and go back n forth as needed? If so do we still need to carry our NFA paperwork around when in its original handgun mares leg configuration?

3. If you engrave your information on the form 1 nfa item, then wish to sell/transfer it to someone else. Will they need to reengrave it? Won’t that create an issue for their nfa tax stamp paperwork?

4. If I create a form 1 nfa weapon as an individual and later want to add it to a new gun trust, how will that affect any engraving?
 
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1. Yes, no different than making any SBR
2. Probably not. The only thing that allows pistol to rifle to pistol is ATF 2011-4, and it specifically admonishes you not to make an SBR.
3. No, No. You transfer it on a form 4 like any other NFA item.
4. It would transfer to your trust on a form 4. No more engraving. $200 tax.
 
2. Are we allowed to remove the rifle stock and replace the original stock to turn it back into a handgun, and go back n forth as needed? If so do we still need to carry our NFA paperwork around when in its original handgun mares leg configuration?

Yes.
With SBRs, if it is in title 1 configuration it will be subject to title 1 rules. Same as if you took an AR SBR and put a 16" barrel on it. This is an easy way to transport your gun across state lines without having to file paperwork (not that the paperwork is difficult).

I don't think you would be required to carry the NFA paperwork if the SBR isn't in NFA configuration. On the other hand, it doesn't hurt to carry it. I have copies of all my paperwork in a binder that goes in my shooting bag any time I go to the range. That way I always know that I have my paperwork regardless of which weapons I'm shooting that day.
 
Yes.
With SBRs, if it is in title 1 configuration it will be subject to title 1 rules. Same as if you took an AR SBR and put a 16" barrel on it. This is an easy way to transport your gun across state lines without having to file paperwork (not that the paperwork is difficult).

I don't think you would be required to carry the NFA paperwork if the SBR isn't in NFA configuration. On the other hand, it doesn't hurt to carry it. I have copies of all my paperwork in a binder that goes in my shooting bag any time I go to the range. That way I always know that I have my paperwork regardless of which weapons I'm shooting that day.

Do you have a cite for that? Can you show anywhere that ATF has said it's OK to go from a pistol to an SBR back to a pistol?

Before 2011-4, ATFs position was clear. As a result of the Thompson suit, ATF issued 2011-4 to give relief from making an NFA weapon when the kit was returned from a rifle to a pistol. No such relief is needed when making an SBR. 2011-4 specifically admonishes you not to build an SBR in the process, whatever the reason, so it does not apply to pistol->SBR->pistol. Without 2011-4, a pistol made from an SBR is still a weapon made from a rifle.

When ATF did have an answer on their FAQ (you can still find this on the internet wayback machine), it ONLY provided the example of SBR to rifle, and did not say you could go back to a pistol.

I have never found a ruling or determination letter that covers returning an SBR to a pistol. If you have, please post it.
 
Do you have a cite for that? Can you show anywhere that ATF has said it's OK to go from a pistol to an SBR back to a pistol?

Before 2011-4, ATFs position was clear. As a result of the Thompson suit, ATF issued 2011-4 to give relief from making an NFA weapon when the kit was returned from a rifle to a pistol. No such relief is needed when making an SBR. 2011-4 specifically admonishes you not to build an SBR in the process, whatever the reason, so it does not apply to pistol->SBR->pistol. Without 2011-4, a pistol made from an SBR is still a weapon made from a rifle.

When ATF did have an answer on their FAQ (you can still find this on the internet wayback machine), it ONLY provided the example of SBR to rifle, and did not say you could go back to a pistol.

I have never found a ruling or determination letter that covers returning an SBR to a pistol. If you have, please post it.

That's an interesting way to read 2011-4. That publication was drafted explicitly to tell people how they can take a pistol, turn it into a rifle, and then turn it back into a pistol again without creating a NFA weapon. The admonishment not to make an SBR is better understood as "don't make an illegal SBR" because it assumes from the beginning that the weapon is not a registered NFA weapon. It also says nothing about how a SBR can be reconfigured and how it should be treated legally after the change.

It would have made no sense for the ATF to include a section regarding what to do if you actually DO have a registered SBR, because that's not what the publication is addressing. 2011-4 should not be used to describe what can and cannot be done with a registered SBR.

This publication is where we get the policy that a Title 1 pistol can be transformed into a rifle and then back to a pistol.

You also reference the ATF FAQ page which showed that a weapon's status as a SBR depends on configuration at that moment, not on whether or not it has been registered with the ATF. That is why you can take a SBR and put a 16"+ barrel on it, and you are only required to follow rules for a Title 1 weapon, not a Title 2 weapon.

So if we combine these two concepts, we have "if it is not configured as a SBR, it is treated as Title 1 and not treated as a SBR" and "if it started as a pistol, it can become a rifle and return to being a pistol", therefore a weapon that started as a pistol and was then made into a SBR can be returned to Title 1 pistol configuration.
 
That's an interesting way to read 2011-4.
It is a literal way to read 2011-4.
That publication was drafted explicitly to tell people how they can take a pistol, turn it into a rifle, and then turn it back into a pistol again without creating a NFA weapon. The admonishment not to make an SBR is better understood as "don't make an illegal SBR" because it assumes from the beginning that the weapon is not a registered NFA weapon. It also says nothing about how a SBR can be reconfigured and how it should be treated legally after the change.

It would have made no sense for the ATF to include a section regarding what to do if you actually DO have a registered SBR, because that's not what the publication is addressing. 2011-4 should not be used to describe what can and cannot be done with a registered SBR.

This publication is where we get the policy that a Title 1 pistol can be transformed into a rifle and then back to a pistol.
You are trying to assume what ATF meant by omitting SBRs from the ruling. It doesn't matter why they did or what makes sense. They did.

You also reference the ATF FAQ page which showed that a weapon's status as a SBR depends on configuration at that moment, not on whether or not it has been registered with the ATF. That is why you can take a SBR and put a 16"+ barrel on it, and you are only required to follow rules for a Title 1 weapon, not a Title 2 weapon.

So if we combine these two concepts, we have "if it is not configured as a SBR, it is treated as Title 1 and not treated as a SBR" and "if it started as a pistol, it can become a rifle and return to being a pistol", therefore a weapon that started as a pistol and was then made into a SBR can be returned to Title 1 pistol configuration.
The actual ruling portion of 2011-4 is this:
Held, a firearm, as defined by the National Firearms Act (NFA), 26 U.S.C. 5845(a)(3), is made when unassembled parts are placed in close proximity in such a way that they:
(a)Serve no useful purpose other than to make a rifle having a barrel or barrels of less than 16 inches in length(e.g., a receiver, an attachable shoulder stock, and barrelof less than 16 inches in length); or
(b)Convert a complete weapon into such an NFA firearm, including
–(1) A pistol and attachable shoulder stock; and
-(2) A rifle with a barrel of 16 inches or more in length, andan attachable barrelof less than 16 inches in length.

Such weapons must be registered and are subject to all requirements of the NFA.

Held further, a firearm, as defined by 26 U.S.C. 5845(a)(3) and (a)(4), is not made when parts in a kit that were originally designed to be configured as both a pistol and a rifle are assembled or re-assembled in a configuration not regulated under the NFA (e.g., as a pistol, or a rifle with a barrel of 16 inches or more in length).

Held further, a firearm, as defined by 26 U.S.C. 5845(a)(3) and (a)(4), is not made when a pistol is attached to a part or parts designed to convert the pistol into a rifle with a barrel of 16 inches or more in length, and the parts are later unassembled in a configuration not regulated under the NFA (e.g., as a pistol).

Held further,a firearm, as defined by 26 U.S.C. 5845(a)(4), is made when a handgun or other weapon with an overall length of less than 26 inches, or a barrel or barrels of less than 16 inches in length, is assembled or produced from a weapon originally assembled or produced only as a rifle. Such weapons must be registered and are subject to all requirements of the NFA


Nowhere does it say that it applies to a SBR.
 
Nowhere does it say that it applies to a SBR.
Agreed, though I think people generally extrapolate that 2011-4 applies to SBRs also. I’ve seen arguments put forth by legally-minded types that made a good case for why you can build a pistol into an SBR and then configure it back into a pistol. But like you said, I’ve never seen the ATF or any court say that explicitly.
 
Agreed, though I think people generally extrapolate that 2011-4 applies to SBRs also. I’ve seen arguments put forth by legally-minded types that made a good case for why you can build a pistol into an SBR and then configure it back into a pistol. But like you said, I’ve never seen the ATF or any court say that explicitly.
I personally believe the rationale ATF used in 2011-4 should apply to SBRs. But that’s just my belief. They would have said so if they meant so.
 
You are trying to assume what ATF meant by omitting SBRs from the ruling. It doesn't matter why they did or what makes sense. They did.

Nowhere does it say that it applies to a SBR.

You're right, they did not address how a SBR can be reconfigured and what rules apply to it in each configuration. This ruling is not about SBRs other than how NOT to make one. So why are you assuming that this ruling limits the configurations of NFA weapons?

It's not about what makes sense (trust me, I'm familiar with how crazy the NFA rulings can be). This is about reading a ruling about one thing and trying to extrapolate a position on something the ruling is not designed to address.


However, if we try to stick with 2011-4...
From ATF 2011-4
Although not defined in the NFA, the term “pistol” is defined by the Act’s implementing regulations, 27 CFR 479.11, as “a weapon originally (emphasis original) 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)” (emphasis added).

...

Therefore, so long as a parts kit or collection of parts is not used to make a firearm regulated under the NFA (e.g., a short-barreled rifle or “any other weapon” as defined by 26 U.S.C. 5845(e)), no NFA firearm is made when the same parts are assembled or re- assembled in a configuration not regulated under the NFA (emphasis added) (e.g., a pistol, or a rifle with a barrel of 16 inches or more in length). Merely assembling and disassembling such a rifle does not result in the making of a new weapon; rather, it is the same rifle in a knockdown condition (i.e., complete as to all component parts). Likewise, because it is the same weapon when reconfigured as a pistol, no “weapon made from a rifle” subject to the NFA has been made. (emphasis added)

The ATF's determination from 2011-4 hinges on the definition of a pistol in the CFR, particularly the "original design" of the firearm, saying that if it was originally designed as a pistol, the weapon may return to a pistol configuration without running afoul of the restriction on "pistol made from a rifle". Nowhere does it say "except for registered SBRs, which will always be treated as SBRs".



Maybe @dogtown tom can shed some light on this. He's usually well versed in this type of regulation.
 
I personally believe the rationale ATF used in 2011-4 should apply to SBRs. But that’s just my belief. They would have said so if they meant so.
I don’t think they’ve taken a stand either way. And I agree that 2011-4 — by itself — doesn’t say that you can configure your Form 1ed SBR back to a pistol if it started off that way. As @Telekinesis pointed out in post #8, the mention of not making SBRs in 2011-4 seems to reference not making an illegal SBR. There’s no mention of going from pistol to legally-registered SBR and back again. Like he pointed out, that has simply been extrapolated from taking the ATF’s stance that an SBR is no longer an SBR when not configured as such and then combining it with Ruling 2011-4.
 
I don’t think they’ve taken a stand either way. And I agree that 2011-4 — by itself — doesn’t say that you can configure your Form 1ed SBR back to a pistol if it started off that way. As @Telekinesis pointed out in post #8, the mention of not making SBRs in 2011-4 seems to reference not making an illegal SBR. There’s no mention of going from pistol to legally-registered SBR and back again. Like he pointed out, that has simply been extrapolated from taking the ATF’s stance that an SBR is no longer an SBR when not configured as such and then combining it with Ruling 2011-4.
People often think of a pistol as not being in an NFA configuration because it has no stock. But a short weapon made from a rifle is an SBR regardless of whether or not it looks like a pistol. If there is no ruling to say that an SBR is not made when you make a weapon from a rifle with less than a 16” barrel, and this weapon is less than 26” OAL, then the weapon made from an SBR (which is a rifle) is an SBR. It’s not in a “title 1 configuration” just because it looks like it is.
 
People often think of a pistol as not being in an NFA configuration because it has no stock. But a short weapon made from a rifle is an SBR regardless of whether or not it looks like a pistol. If there is no ruling to say that an SBR is not made when you make a weapon from a rifle with less than a 16” barrel, and this weapon is less than 26” OAL, then the weapon made from an SBR (which is a rifle) is an SBR. It’s not in a “title 1 configuration” just because it looks like it is.
Yes, but I think the argument many people make is that since an SBR is a type of rifle, the concepts laid forth in 2011-4 apply to SBRs as well as to rifles.

Also, the ATF’s stance that an SBR is only treated as an SBR when in SBR configuration strongly implies that 2011-4 applies to SBRs also. Think of this scenario: Say you have a Form 1 SBR (that started its life as a pistol) and then you install a 16” barrel on it. At that point, it’s a regular Title 1 rifle and treated as such per the ATF. So why couldn’t you then configure it as a pistol per 2011-4?
 
Yes, but I think the argument many people make is that since an SBR is a type of rifle, the concepts laid forth in 2011-4 apply to SBRs as well as to rifles.

Also, the ATF’s stance that an SBR is only treated as an SBR when in SBR configuration strongly implies that 2011-4 applies to SBRs also. Think of this scenario: Say you have a Form 1 SBR (that started its life as a pistol) and then you install a 16” barrel on it. At that point, it’s a regular Title 1 rifle and treated as such per the ATF. So why couldn’t you then configure it as a pistol per 2011-4?
I agree, but you have to remember a couple things:
ATF didn’t come up with 2011-4 because they wanted life to be easier for us.
ATF didn’t casually exclude SBRs. Regardless of whether you can rationalize that it should apply to SBRs (and I can, especially as telekinesis pointed out ATFs use of “originally” in the pistol definition), ATF not only didn’t include SBRs, they specifically excluded them. Had the ruling just been mute on the subject, it could easily be reasoned that it applies. It doesn’t matter why we think they excluded SBRs, they did, deliberately.
 
People often think of a pistol as not being in an NFA configuration because it has no stock. But a short weapon made from a rifle is an SBR regardless of whether or not it looks like a pistol. If there is no ruling to say that an SBR is not made when you make a weapon from a rifle with less than a 16” barrel, and this weapon is less than 26” OAL, then the weapon made from an SBR (which is a rifle) is an SBR. It’s not in a “title 1 configuration” just because it looks like it is.

Keep in mind that the Mares Leg, from Henry or even Rossi is define by the ATF as an official handgun and is designed and sold as a handgun. But by adding a true rifle butt stock, it does officially make it an SBR and must be done via a Form 1.
That much I do know.

But if it were possible to add a longer barrel 16” or longer, it would make it a title 1 rifle.
Even if I took the Mares Leg and at the same time added both the Butt stock and the longer barrel, then it would go straight from handgun to rifle with no SBR creation along the way. Thus no form 1 needed.

The way I see it from what everyone has said, is that I can in fact take it from title 1 handgun to form 1 SBR and then go back n forth as desired.

I had the attorney who is doing my gun trust do some research on it. As far as he is concerned, he has not been able to find anything prohibiting me from going back n forth between title 1 handgun and form 1 SBR. He said though I should keep a copy of my tax stamp with me at all times that I have both the mares leg AND the butt stock with me even if it is NOT installed and in an SBR configuration. Why? Because I will have the engraving on the gun, and the stock in my possession.

Now he went on to say though, that being the ATF they could change their position on being able to do that in the future.
 
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other then the “coolness” factor of it.... I’m not really sure that adding a rifle stock to the Mares leg and having the capability to go between SBR and handgun would be of any major benefit in shooting or accuracy.

My accuracy at 50 yard is pretty darn good. I can easily hit a possum at 50, and my accuracy at 100 yards isn’t to bad either. Not sure if adding the stock would increase my accuracy at 100 yards that much. Who knows. I don’t lol
 
I'm sorry I never addressed the question on the conversion of a mares leg type firearm or other SBR/SBS that become that by the addition of a stock.

pjeski is correct; once registered and converted into SBR or SBS, these weapons are now rifles or shotguns, and cannot be legally reconfigured into a pistol or "other" firearm. You can certainly take the stock off and use it as a pistol, but legally it is still an SBR/SBS and all NFA rules apply. Once made into an SBR/SBS, there is no avenue by which the firearm can be a pistol or "other" firearm again; the only way to make them title I is to fit them with the respective 16" or 18" barrels (or permanent muzzle devices/extensions to get to that length) and ensure >26" OAL. If the purpose of reconfiguring to title I is the sale of the firearm, you need to first detail the permanent change in a letter to ATF and have it struck from the registry. And no, they will not refund your $200 tax. When the weapon is made, that's gone forever.

I also misspoke slightly in talking about repair of silencers by the F1 maker. You can repair them, but you cannot manufacture any new parts without a new F1 for that part. So, yes, you could shorten & re-thread a damaged tube or weld a cracked tube yourself, and you could beat a damaged baffle back into shape or make alterations to it such as changing the clip style or adding ports, but manufacturing a baffle or any other part has to be done by an SOT to avoid a new stamp per part. Certain mounts or caps that are sold commercially as non-NFA (because they also fit non-NFA muzzle devices) can be possessed individually and installed on your F1 or F4 silencer.

Having said that, there is a legal end-run you can do that enables you to have some replacement parts that aren't actually spare parts under the law. It's a bit convoluted, but if you make, say, a 16" modular suppressor, and the front half is a solid stack of baffles, you can use the can only in the shorter configuration, and you could replace any damaged baffles in the primary tube with baffles from the extension module. You just have to be able to configure the thing into it's full F1 listed length at any time, and you have to make sure that the front module is not something which could become another silencer just by installing a mount, because that can be construed as constructive possession. This route has also been used by F1 makers who wanted to experiment with different baffle types and spacing configurations without multiple stamps. It's perfectly legal as long as you can assemble that full length and there are no parts left over when it is so-assembled.

Also, a note on F1 silencer overall length: Be reasonably accurate, but you do not have to nail it down to .005 or even 1/4". In terms of F1, ATF has maintained for some time that +/- 1" is in the acceptable range (have even told some people 2"). If you registered as a 7" and it's going to turn out to be 5" or 9", though, you need to send an amendment letter before finalizing construction detailing the change. Once built, length and caliber cannot be amended. Contrary to popular belief that they can be shortened any amount just not lengthened, significant shortening is really only acceptable if they have been significantly damaged to a degree necessitating the alterations. As a manufacturer, I will not shorten any silencer by more than 1" unless there is legitimate, documentable damage requiring more.

In terms of F1 silencer caliber, lots of confusion abounds. The caliber on the F1 denotes the minimum bore size of your can. You cannot built a .30 caliber silencer with a .28" bore. But there is no maximum bore size for a given caliber, and you can fire any caliber through it you like (obviously you need to ensure there is enough clearance). It's perfectly legal to use a .30 cal on a .223, .243, etc. There's also nothing legally prohibiting you from running a .30 cal can on a .338 if the aperture size is large enough. Lots of cans are significantly overbored to reduce back pressure or mitigate baffle strike issues on certain hosts. For example, I bore .30 cal cans going on AKs and other combloc guns to 7/16" (.4375"). This is done partly to lower piston and port pop, but mostly because many (most) AK barrel threads are only sorta concentric and aligned at best. Of course, that's a large enough bore for .375" caliber rounds on hosts with good alignment. 5.56 cans for autoloaders I bore to .320" to keep port noise down, and that's a safe diameter for up to 6.5mm projectiles.
 
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