Optimal 5.56 AR Pistol Barrel Length

I prefer the 8.5 over the 10.5 barrel on a pistol build. I see the pistol build as the gun to get you from the vehicle to the house. I tried the 10.5 barrel but found the 8.5 barrel to be better suited.

When I built mine + 3 years ago, 10.5 was supposed to be the minimum for reliability with 5.56. I built mine with carbine gas, nitride treatment, from Radical Firearms. Ran without a single failure until I traded it. YMMV.

My 6.8 and 5.56 hunting SBR uppers are 10.5”.

gbw said:

Any particular reason why? Thanks

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Balance, in multiple aspects. Physical balance in hand and intrinsic balance of “short enough to not be almost rifle/carbine length, but not so short it loses utility.” With a brake or a can out front, a 10.5” is still a short and handy carbine length. It’s also accepting of a full length rail for comfortable and natural support hand placement - not choking down on a magwell grip as a guy might be stuck with a 7” stick.

I have and have had 7, 8.5, 9, 10.5, 11.5, 12.5”, and 14.5” pistols/SBR’s in various cartridges, I tend to come back to 10.5”.

I have only handled one AR pistol. My 10.5" 5.56. Illllllike it.
Of my four ARs, it's my favorite.
Shown here with .22lr conversion kit.

I too prefer the 10.5 inch barrel for most tasks (hunting, work, etc.).

I would go with 10.5". The shorter pistol gas tube systems seem to be problematic, or at least picky with certain ammo. We were issued a 10.5" MK18 upper in the military and they did very well with M193, green tip, and MK 262.

I run a 11.5" (BCM), I still like the 10.3/10.5" (Colt/LMT) for compactness and handling, but read this from the owner of BCM.

https://www.ar15.com/forums/industry/_Q__Why_BCM_chose_the_11_5_SBR_over_the_10_5_/138-174764/

I know BCM only offers the 11.5" and their reasons are sound, but I just don't buy the benefits of dwell time is really that significant. While even the 10-11.5" barrels are still loud if unsuppressed, my 8" 5.56mm can be quite concussive. For me, I just really like the 10.5" length the best.



ROCK6

I really like your "rollout kit"!!

10.5 inch.

Like the others have said it just feels right and I like that length the best in terms of balance.

Great thread, thanks OP, made my decision easy.

If I may follow up, what are y’all running as far as gas? Is there a particular barrel manufacturer for 10.5” that is known to work well with only buffer and spring changes and not requiring adjustable gas? One tenet of my defensive carbine build guidelines is no adjustable gas system.

Doc7 said:

Great thread, thanks OP, made my decision easy.

If I may follow up, what are y’all running as far as gas? Is there a particular barrel manufacturer for 10.5” that is known to work well with only buffer and spring changes and not requiring adjustable gas? One tenet of my defensive carbine build guidelines is no adjustable gas system.

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I’ve used the carbine gas system on both of mine.

One is a PSA 10.5” FrankenAR and the other one was an 11.5” BCM (sold it due to lack o funds, it was worth more in a sale).

With brass cased ammo I haven’t had an issue with either. On the PSA I ended up with two stuck Tula cases early on after switching from brass in a dirty gun, but that’s a fairly common issue. After I stuck with brass cased ammo I’ve never had any issues whatsoever.

The BCM never saw anything but brass.

Always felt the 10.5” was slightly better balanced, but it wasn’t a huge issue on either.

I prefer brands like Colt, LMT, BCM, DD for shorty's. With other brands of unk origins, the AR15 world is an incestuous one, you never know what you are getting. I remember back during the "dark ages" you just cut down a barrel, drilled a new gas port in incremental sizes till the gun ran, and repositioned the FSH and pinned it. They typically were over-gassed and it beat the crap out of the guns. This is with a standard music wire buffer spring and CAR buffer because that's all you had back then (30+).

I use an H buffer and CS buffer spring, BCM bolt/carrier with the extra power extractor spring and Viton donut. I am not running suppressed. With all the different buffer weights, and spring options, proper gas port sizing, you can "dial in" your gun

Recently PSA has 7 and 7.5" Pistol uppers. Although like most of their kits, have a hard time keeping them in stock. Based on Youtube video research you are also pushing the reliability question of the system going that short. Fortunately my LGS had a 8.5" AR pistol in the last time I grabbed some snake ammo. That seemed really well balanced for me and that will likely be my build if I ever get around to it.

What i have concluded is that anything shorter than 10" is more suited for the duty of "range toy" due to the loss of velocity and the intense concussion. 9mm and 300 blackout are a better choice for the shorties. I have a couple ar pistols set up in 5.56 with 10.5" barrels and flash can devices on the front that make them more bearable to shoot. The idea is that should i need to defend myself with one, I might not have time for ear protection and the less deaf and disoriented i become the better.

When I built mine + 3 years ago, 10.5 was supposed to be the minimum for reliability with 5.56. I built mine with carbine gas, nitride treatment, from Radical Firearms. Ran without a single failure until I traded it. YMMV.

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Mine is a Stag, 7.5" bought as an assembled upper; ran perfect from the first shot, whatever ammo I've tried (well, except for some Trail Boss reloads which make it a single shot).

My 5.56 Delta Level Defense ECAR ‘other’ has an 11.5” barrel with a 1” flash suppressor. I have heard for a longtime going less than 10.5” and you loose a lot of juice. I live in jurisdiction (CT) where my options are limited. It was the best I could do for the money. The manufacturer had to meet length requirements in order to make it work. So far it works just fine. I can put the 5.56 bullet just about anywhere I want. So far my range and accuracy is limited only by my personal skill, vision and available acreage.

This is the only photo I have from its birthday.

ancientnoob said:

This is the only photo I have from its birthday.

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Is the short vertical fore grip pictured not considered one? I was under the impression that a vertical foregrip on a AR pistol no longer made it a pistol, legally. Which is why many set ups use the angled fore grip.

herrwalther said:

Is the short vertical fore grip pictured not considered one? I was under the impression that a vertical foregrip on a AR pistol no longer made it a pistol, legally. Which is why many set ups use the angled fore grip.

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Correct, it is either a Firearm or an Any Other Weapon. Which one it is depends upon overall length. In MANY but certainly not all cases, a ~10” barrel gets you to the 26” overall length. I don’t know for certain but the photo above appears to be a Firearm, not a pistol, not a rifle, and not an Any Other Weapon. The poster who put the pic up says it was an “other” in quotes but I do not believe he is referring to a register “Any Other Weapon”, because if he was, there wouldn’t have been any length concerns that he also mentioned. An AOW could have been as short as desired.

https://www.ar15.com/forums/AR-15/Fore-grips-on-ARs-with-braces-/118-741488/

Here is a graphic from that post, see the bottom 2 pics:

Doc7 said:

Correct, it is either a Firearm or an Any Other Weapon. Which one it is depends upon overall length. In MANY but certainly not all cases, a ~10” barrel gets you to the 26” overall length. I don’t know for certain but the photo above appears to be a Firearm, not a pistol, not a rifle, and not an Any Other Weapon. The poster who put the pic up says it was an “other” in quotes but I do not believe he is referring to a register “Any Other Weapon”, because if he was, there wouldn’t have been any length concerns that he also mentioned. An AOW could have been as short as desired.

https://www.ar15.com/forums/AR-15/Fore-grips-on-ARs-with-braces-/118-741488/

Here is a graphic from that post, see the bottom 2 pics:
View attachment 847788

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It is considered and manufactured, bought at an LGS on early production run as a "Firearm." It is not a pistol, never made as one, not rifle not shouldered and not made as one. It is not an AOW. It was legally purchased and transferred at LGS and they are becoming common occurrences in all the shops.

My post was meant to comment on the 5.56 x45 mm performance out a barrel of said length. I apologize for derailing.

i went with 10.5" because i wanted a fixed FSB and a carbine length handgaurd is the shortest that i am comfortable with. mine is a PSA upper that i am using it with a carbine buffer and carbine spring and it is much smoother than i was expecting it to be. it is compact enough that it makes a huge difference over my 16" and i really enjoy it for 0-100 yard shooting (i am confident that i could go to 200 but have not had the opportunity yet).

I have played with 7.5", 10.5", and 11.5". I built the 11.5 for myself. I want a 10.5, the 7.5 I labeled "a personal flashbang" it was very loud and bright! Felt like getting punched in the face when shooting it on my sbr lower. Too flashy.