What does it take to change a 9mm rifle into a 9mm pistol

[bill4321]

Hello all,

Long time lurker and 1st time poster here.

I have a stock 9mm AR rifle that was commercially made by CMMG and I was thinking about making it into a SBR. However the more I read up on that the more I think I would rather just try to convert it into a AR pistol with a SIG brace and avoid the NFA paperwork/tax for right now.

However, unlike most of you I have never built an AR style firearm from the ground up. I have done simple things like change out a trigger, swap out furniture, and mount optics....but never attempted to install or alter any parts that make or break the reliability/functioning of an AR before. So please forgive me if I ask a question that you all might think is rudimentary.

So with that said.....what would it take to convert this 16" 9mm rifle into a 5" 9mm pistol?

1. My understanding is that once the lower has been made into a rifle that it can't be made into a pistol. So I would have to buy another CMMG lower correct? I want to stay with CMMG lower because I do not want any kind of mag-well block, plus I already have several of the colt/uzi magazines.

2. Also how/when exactly does an AR lower get declared as a pistol versus a rifle? I have never bought just a lower before, so I was thinking that happens when you go through your background check when you pick up the item from your FFL...is that correct? Or are rifle and pistol lowers actually different in some way?

3. What all is involved with putting a 5" barrel onto an upper? I assume this is something that requires the right tools to torque down properly. Is there anything else involved with that to make the firearm safe and reliable? I assume if I take a barrel and upper to my local gunsmith he can put them together for a reasonable fee. Or is this something that can be done yourself by a 1st timer?

4. Also I would need to put on a specific pistol buffer tube correct? One that doesn't have the indents for a stock to attach to? But I can just reuse the spring and buffer that are in the rifle now correct?


Is there anything else that would be involved with making a rifle into a pistol? Don't be afraid to hurt my feeling ! I am asking because I don't know.


I thought about just selling this 16" rifle and buying a factory made AR pistol from CMMG, but they all have 8.5" barrels and I am wanting a 5" barrel (I might down the road I decide to suppress this and have read that 5" is probably the best to keep the heavier 9mm subsonic). So since even if I bought a complete factory built AR pistol, it would have to be even further modified to get what I want.....I was thinking about just trying to modify the rifle I already own.

Or should I just bite the bullet and go the SBR route?

Thanks again for any input and advice you all can give me.

[Caduceus]

Hello all,

Long time lurker and 1st time poster here.

I have a stock 9mm AR rifle that was commercially made by CMMG and I was thinking about making it into a SBR. However the more I read up on that the more I think I would rather just try to convert it into a AR pistol with a SIG brace and avoid the NFA paperwork/tax for right now.

However, unlike most of you I have never built an AR style firearm from the ground up. I have done simple things like change out a trigger, swap out furniture, and mount optics....but never attempted to install or alter any parts that make or break the reliability/functioning of an AR before. So please forgive me if I ask a question that you all might think is rudimentary.

So with that said.....what would it take to convert this 16" 9mm rifle into a 5" 9mm pistol?

1. My understanding is that once the lower has been made into a rifle that it can't be made into a pistol. So I would have to buy another CMMG lower correct? I want to stay with CMMG lower because I do not want any kind of mag-well block, plus I already have several of the colt/uzi magazines.

2. Also how/when exactly does an AR lower get declared as a pistol versus a rifle? I have never bought just a lower before, so I was thinking that happens when you go through your background check when you pick up the item from your FFL...is that correct? Or are rifle and pistol lowers actually different in some way?

3. What all is involved with putting a 5" barrel onto an upper? I assume this is something that requires the right tools to torque down properly. Is there anything else involved with that to make the firearm safe and reliable? I assume if I take a barrel and upper to my local gunsmith he can put them together for a reasonable fee. Or is this something that can be done yourself by a 1st timer?

4. Also I would need to put on a specific pistol buffer tube correct? One that doesn't have the indents for a stock to attach to? But I can just reuse the spring and buffer that are in the rifle now correct?


Is there anything else that would be involved with making a rifle into a pistol? Don't be afraid to hurt my feeling ! I am asking because I don't know.


I thought about just selling this 16" rifle and buying a factory made AR pistol from CMMG, but they all have 8.5" barrels and I am wanting a 5" barrel (I might down the road I decide to suppress this and have read that 5" is probably the best to keep the heavier 9mm subsonic). So since even if I bought a complete factory built AR pistol, it would have to be even further modified to get what I want.....I was thinking about just trying to modify the rifle I already own.

Or should I just bite the bullet and go the SBR route?

Thanks again for any input and advice you all can give me.

Well most people will tell you just to go SBR and call it good. It'll certainly be cheaper than a pistol.

But, yes, just buy a CMMG lower (complete or stripped doesn't matter, as long as it's never had an upper placed on it, and designated an "other" on the 4473). You don't technically need to have a pistol buffer tube versus a standard carbine or rifle buffer tube. The big no-no seems to be having a barrel > 16 inches and then putting a regular stock back on; that classifies it as a rifle. If the upper has a barrel < 16 inches with a stock, that's a SBR. But get that lower, take off the stock, and THEN put on a sub-16 inch upper ... pistol. Weird and a bit arbitrary, I know.

Swapping out barrels requires some know-how, which I don't have. You can probably also buy a built upper or have ADCO cut one down.

Or, since you're looking at a 5 inch barrel, just buy a regular pistol with a 5 inch barrel.

[jwsturr]

Send the barrel out to have it cut to the length desired. Change the buffer tube to a pistol buffer tube. If you want to go sbr route. You need to set up a gun trust. Pay the $200 tax and wait for the paperwork. The sig brace is a way to circumvent the tax.

[wildcard600]

Send the barrel out to have it cut to the length desired. Change the buffer tube to a pistol buffer tube. If you want to go sbr route. You need to set up a gun trust. Pay the $200 tax and wait for the paperwork. The sig brace is a way to circumvent the tax.

his current lower is a rifle lower. to do what you propose would be a federal crime.

[jwsturr]

I skipped the "commercially" made part. Reading is fundamental.

his current lower is a rifle lower. to do what you propose would be a federal crime.

[ezveedub]

Your CMMG 9mm rifle would have to be registered as a SBR. You cannot convert an originally built rifle to a pistol without violating ATF/NFA regulations.

[bill4321]

Thanks for the input everybody.

After thinking it over, I have decided to just build an AR pistol from the ground up with all new parts. That way I don't have to worry about how the lower was originally classified. And then I can have the rifle as a rifle and the pistol as a pistol.

I want to do the paper work and stamp for a SBR so that I can change my current rifle into a SBR someday down the road. But first I need to read up on how to create a trust so that my better half can also have access to any NFA items.

Thanks again everybody !

[ezveedub]

If you build a stripped lower into a pistol first, it can be changed to rifle and back to a pistol, but never a rifle first or originally a rifle from the manufacturer to a pistol without registering it.

[bill4321]

For what its worth....I guess I should have clarified what I was originally trying to do.

My better half is not very proficient with her 9mm pistol. I know that is something that can be improved with practice, but honestly she just won't do it. However she loves shooting the 9mm AR with an Eotech on it. And she is pretty good with it at close range. The problem is that it is too heavy for her standing and firing offhand for very long.

My thought was to make something more compact and lightweight for her, so that is what made me think of reading up on SBRs. I wanted to see if I could get the full-size 9mmAR into something more fitting to her so she would practice with it more and become even more proficient with it (for the possibility she would ever have to use it in a home defense situation). But then that opened up the whole can of worms about having NFA type items and also who would have access to them and all that jazz. I thought going the AR pistol route might be the best option since it would technically just be a pistol in court, if god forbid she ever had to use it, versus a NFA type item.

But as it stand now...I am going to make a 9mmAR pistol from scratch and then have both the full size rifle and then also a shorter and hopefully lighter weight 9mm AR pistol.

I guess I'll stop rambling now.

Thanks again everybody for your input and feel free to offer up any further suggestions/tips you might have.