AR pistol into a carbine.

[CraigS]

I have been thinking about an AR pistol. Then I started thinking about an AR carbine in 9mm to shoot PCC in idpa. So Maybe an AR pistol in 9mm? These are guns I'd like to try but I am not sure if I would use long term. So Q#1. If one buys an AR pistol (any caliber) is it legal (ATF not IDPA) to turn it into a carbine w/ a carbine barrel and stock? Q#2. Is it even possible or do they make the mating portions different so a carbine barrel won't fit a pistol upper? I ask because my Buckmark rifle can not mount the barrel from my Buckmark pistols or vice versa. Are there certain brands of pistols that are that are manufactured to AR standards so carbine parts will fit the basic upper and lower or are all pistols made so this type of swapping doesn't work?
Q#3. If all the above isn't feasible do you have recommendations for a 9mm AR carbine that works out of the box. I keep hearing guys talk about changing parts but haven't been clear if they did it because the gun didn't run or just because they wanted something different. Thanks for your thoughts.

[psalms144.1]

Craig - I'm not a lawyer, or an ATF inspector or agent, but this is what I've been told by several: it's is totally possible and legal to put a carbine length upper on an AR9 lower. That does NOT make your AR9 a carbine - just a very long barreled pistol.

IF, however, you change your brace or bare tube into an actual rifle STOCK, then you cannot ever put a "pistol" length upper back on it, even if you switch the receiver back to the brace. Once a "rifle," always a "rifle," in the eyes of the law. To go back to sub-16" barrel length legally, you would have to register it as an SBR.

I've got quite a few rounds through a Foxtrot Mike FM-9 with 7" barrel and SBA3 - it does EVERYTHING I want/need a PCC to do, include feeding reliably from Glock magazines and locking open on an empty magazine. Lots of other lower end AR9s don't have last round bolt hold open.

[MistWolf]

IF, however, you change your brace or bare tube into an actual rifle STOCK, then you cannot ever put a "pistol" length upper back on it, even if you switch the receiver back to the brace. Once a "rifle," always a "rifle," in the eyes of the law. To go back to sub-16" barrel length legally, you would have to register it as an SBR.

This is incorrect. A pistol may be configured as a rifle, then reconfigured as a pistol, so long as at no time is the pistol in an illegal configuration during the process.

[Norville]

This is incorrect. A pistol may be configured as a rifle, then reconfigured as a pistol, so long as at no time is the pistol in an illegal configuration during the process.

This has always been my understanding. The general advice was build or buy the pistol first , then you can create a legal rifle from it with the appropriate barrel. Be sure to not reinstall the pistol upper before removal of the buttstock or you have created an unregistered SBR.

AR uppers and lowers generally interchange, I am not aware of specific pistol or rifle receivers.

My Sig MPX carbine has been quite reliable although others have had parts breakage issues.

[psalms144.1]

This is incorrect. A pistol may be configured as a rifle, then reconfigured as a pistol, so long as at no time is the pistol in an illegal configuration during the process.

I stand corrected. I'll make sure to educate my ATF contacts as well...

[dontshakepandas]

I stand corrected. I'll make sure to educate my ATF contacts as well...

I think the key point here is that it must start as a pistol to be able to go back to the pistol configuration. If you purchase something or build it initially in a rifle configuration, it must stay a rifle. If you buy/build as a pistol first, you can go back and forth.

Pistol > Rifle > Pistol is ok
Rifle > Pistol is NOT ok

All of the above is stupid as hell.

[WobblyPossum]

This is incorrect. A pistol may be configured as a rifle, then reconfigured as a pistol, so long as at no time is the pistol in an illegal configuration during the process.

I stand corrected. I'll make sure to educate my ATF contacts as well...

I believe Mistwolf is correct. Here is a link to ATF’s website which includes a link to the actual document cited: https://www.atf.gov/firearms/qa/can-...tering-firearm.

[CraigS]

Ok, so you separate the pistol upper and lower. Change the barrel on the upper and change the stock on the lower and reassemble upper and lower. A long as both barrel and stock are swapped before reassembling the upper and lower you are good to go. I can live w/ that. Thanks guys.

[Screwball]

Ok, so you separate the pistol upper and lower. Change the barrel on the upper and change the stock on the lower and reassemble upper and lower. A long as both barrel and stock are swapped before reassembling the upper and lower you are good to go. I can live w/ that. Thanks guys.

Make sure a 16” barrel is installed before you put a stock on it and that the stock is off before you put a barrel less than 16” back on… easiest way to describe it.

Stupid, but so are the NFA and the GCA.

[Caballoflaco]

Ok, so you separate the pistol upper and lower. Change the barrel on the upper and change the stock on the lower and reassemble upper and lower. A long as both barrel and stock are swapped before reassembling the upper and lower you are good to go. I can live w/ that. Thanks guys.

Just buy a different complete upper with a 16” barrel made by a quality manufacturer. Then all you do is remove brace from pistol, remover the pistol upper. Install the rifle upper. Install the stock.

Changing barrels is an armorer-level task that requires special tools and knowledge to do correctly.

Also with two uppers you can then keep a dedicated optic on each upper and not worry about re-zeroing when you change configurations.