ideal AR pistol barrel length


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USAF_Vet
October 30, 2013, 07:27 PM
I'm starting a bottom up AR pistol build. I have a fair amount of experience with AR roles ad carbines, but this will be my first pistol. I plan to buy a prebuilt upper, but which length should I go with?
Anything at 11"+ puts the OAL over 26" with most pistol buffers I have measured, so I'm leaning towards a sub 11" barrel.

Caliber will be standard 5.56 / .223


Also, this upper may be used in the future if Michigan ever approves SBRs, so keep that in mind.

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MachIVshooter
October 30, 2013, 09:03 PM
Anything at 11"+ puts the OAL over 26" with most pistol buffers I have measured, so I'm leaning towards a sub 11" barrel.

It's perfectly legal to have a handgun over 26"; NFA only applies to rifles or shotguns under 26". You could build a "pistol" with a 60" barrel if you desired, and it would still be considered a title I handgun, so long as you didn't attach a shoulder stock.

Having said that, AR pistols are kind of ungainly as it is, so I would suggest keeping the barrel pretty short, like 7.5".

I also like the 7.5" on my SBR, though the 12.5" is more useful.

7.5":

http://i110.photobucket.com/albums/n117/Hunter2506/101_1779_zps36fe7140.jpg

12.5":

http://i110.photobucket.com/albums/n117/Hunter2506/101_1778_zpsc4d258cd.jpg

Gordon
October 31, 2013, 12:38 AM
You need a pistol length gas system to operate under about 9.5" . A 12" barrel is pretty close in performance to a 14.5". An 11" barrel works well with Carbine length gas systems. I have a Noveske Diplomat 7.5" Pistol which is extremely accurate and reliable but has a 3" KX-3 on it to be shootable without a suppressor.

460Kodiak
October 31, 2013, 12:52 AM
I had a sig P556 with a 10 inch bbl and 1:7 twist rate. Plenty accurate nice balance.

USAF_Vet
October 31, 2013, 08:41 AM
It's perfectly legal to have a handgun over 26"; NFA only applies to rifles or shotguns under 26". You could build a "pistol" with a 60" barrel if you desired, and it would still be considered a title I handgun, so long as you didn't attach a shoulder stock.

I was under the impression that a pistol with +26" OAL was a title I 'other firearm'. I knew it was not NFA. There was a thread a few weeks ago with the AR stabilizing wrist brace, with a VFG, where the firearm was +26" OAL.

Having said that, AR pistols are kind of ungainly as it is, so I would suggest keeping the barrel pretty short, like 7.5".

That's what I was leaning toward, for the same reason. A pre-made 7.5" upper should be good to go to slap on a pistol lower and be ready to fire. I will not be assembling the upper from a stripped receiver.

Is there anything on the market in an even shorter barrel configuration, or does the extremely shirt gas system not allow for such short barrels?

Big Bad Bob
October 31, 2013, 09:27 AM
For AR pistols chambered in 5.56 the question of barrel lengths comes down to 2 things for me, muzzle velocity and intended use. Sorry to hear you don't live in a "free" state and cant have an SBR, when folks tell me they are building an AR pistol I always suggest dropping a Form1 on an SBR, sorry that is not an option for you. Remember that an AR pistol needs to be built on a virgin lower and the lower needs to registered as a pistol and not a rifle. Just FYI.

Shortening the barrel is going to reduce your MV and likewise your ft/lbs of kinetic energy. When first designed the AR-15 and .223's optimal barrel length was determined to be 20", that said look below you will see the corresponding pistol length barrels and MV's to carbine and rifle length.

BBL___ 77 gr__M855 62 gr__XM193 55 gr
7.5"_____2053________2244________2364
10.5"____2363________2639________2755
14.5"____2576________2861________2984
16"_____2669________2938________3075
20"_____2818________3061________3254

Now that you have an idea of the MV reduction of pistol length barrels, the question of intended use comes in. If this is a plinker, than what will be most comfortable and controllable to shoot is your preference. I have seen 10.5" AR pistols shoot out to 300 meters believe or not quite accurately. If this home defense/protection I would go with what will be the easiest for you to maneuver. My preference for AR pistols is no shorter than 10.5 because of the MV reduction drops off a good bit below that. Its all up to you.

May I also suggest that if your state never legalizes SBR's look into the perfectly legal Sig AR pistol brace.

USAF_Vet
October 31, 2013, 10:55 AM
Bob, I am building it from a stripped virigin Aero Precision lower. Since Michigan does require pistol registration, it will be done as such.
This will probably just be a range toy, but also a candidate for an SBR if they are ever approved. Rumor is we get closer and closer each year.

Thanks for posting the info on muzzle velocity. I'm still leaning toward 7.5" since I don't plan on shooting much beyond 100 yards with this set up. The Sig stabilizer brace is on my list of things to get, even if we do get SBRs. This is being built and registered as a pistol for the sole reason of being able to legally switch from pistol to rifle configuration.

Big Bad Bob
October 31, 2013, 02:23 PM
Good stuff,

my apologies if you already knew about the virgin lower and pistol to rifle conversions and vice versa. I keep meeting alot of folks who arent aware of those issues and just wanted to clarify. Running afoul of the ATF is not a good thing and they dont acknowledge ignorance of the law.

One thing I would add is to get a good muzzle brake, Noveske KX3 Krink, PWS etc to help with muzzle rise.

Have fun. Hoped the info helped.

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