Shortest 5.56 barrel

General Firearms NFA
1

For a long time 11.5 or larger was considered the shortest reliable length with some 10.5 inch barrels being considered acceptable. but as we all know, a LOT has changed in the industry in the last few years.

So currently I am running a 12.5 inch barrel on my AR “pistol”. I have been pretty happy with this but I would really like to go shorter and I have seen a few as short as 7.5 around here but we all know that most people don’t shoot enough to know if something is reliable so I thought I would reach out to the hive mind.

Are there any reliable shorter barrels out there on the market or should I just continue to play it safe.

To be clear this is a weapon that stays in my car for “oh shit” times. So Less than ideal reliability is not acceptable.

2

I believe a 7.5" 5.56 Pistol gas can be reliable, as in “goes BANG” most every time.

The gas system timing is not bad, but the pressures are quite high.

It has roughly double the available gas drive of a 16" midlength, so the gas port needs to be very small.

That has its own issues around sensitivity to tolerances and wear.

IMO, if a 7.5" barrel is a requirement, then 300 BLK is a very good answer.

If 5.56 is a requirement, then 10.5" to 11.5" is an effective minimum barrel length for good terminal effectiveness with common ammo.

Specific bonded and monolithic ammo can help the 7.5", but at ~2000 fps, terminal performance will not be spectacular.

Also, blast and flash will be terrible without a suppressor or a linear muzzle device like our Covert Comp.

3

Once you get into the sub 10 inch 5.56 AR game you need to look at pistons.

My pws Diablo 7.75" piston upper is accurate and reliable. 3" or so groups at 100y with 77gr OTM and never a hiccup. I’ve shot 7" and 8* DI guns and they aren’t even close. The DI system, in my opinion, isn’t designed to be run with that small of a barrel.

Now 300blackout is a totally different story. 8" .300 DI is going to be perfectly reliable if you get quality parts and consistent ammo. It’s designed to run that way and accurately.

4

I disagree about the piston thing w/o a discussion about firing schedule.

For a sub 10" with a light firing schedule there is no reason to think a DI used in the OP’s role wouldn’t be reliable.

All that being said, I think there are MUCH better choices that would exist in that requirement.

5

Considering all the negatives, I wouldn’t go below 10.3". If you get the desire, then go to .300 Blackout.

6

Wish I could have an SBR, but I live in a Commie State

7

Came in to post this. You loose a lot of velocity and get to the bottom threshold of even the best rounds (terminal ballistics), but are now in the optimum length for 300blk.

8

Nothing wrong with a 7" for what it is. Truck gun or home defense isn’t a bad option imo but I’d keep 10.5-11.5 for anything else.

I keep electronic earpro with it at all times bc #1, I can amplify my hearing, #2 you won’t blow your eardrums to smithereens.

I wouldn’t personally build a upper that short unless you think you can build one reliable. My PWS diablo is a running machine whatever you throw at it. If you decide to go this short, PWS or DD diplomat.

9

When the atf let’s me I will put together my 7.5" 5.56 sbr. I think that it is a suitable platform for specific rolls. I realize that 300blk or 6.8spc even work better in super short barrels but I refuse to have an AR that doesn’t use 5.56 as I don’t want the hassle of different ammo or magazine segregation. I wanted the shortest possible length without resorting to folding stocks or proprietary pdw stocks. I get that 5.56 going 2000 fps isn’t going to be the most effective man stopper but 30 of that is going to have more range than 15 9mm. For a niche weapon I think it can be very useful. This is all speculation until I get mine together and run it through its paces. As to the blast and flash I’m going to be using a B.E. Meyers 249 flash hider. If it doesn’t work as I want it is as easy as a 10.5" barrel swap.

10

But 30 9mm JHP in a MP5 / Scorpion / MPX would probably be a lot more practical and effective, especially considering the muzzle blast and noise.