Assuming you haven’t done it yet, I would personally suggest against going that short for a 5.56. For me 16 inches is my cut off with 5.56 chambered barrels. You’re gonna get increased muzzle flash and pressure.
But you do you, and a 5.56 is still more effective than a 9mm.
You are better off for that length IMO to go with 300AAC BLK which was designed for shorter barrels. 300AAC comes with sub-sonic loads as well. Plus if you do get a suppressor, 300AAC BLK works beautifully with suppressors.
10.5 is the shortest i would ever go, i have a couple in this length and anything under 150-200 yards with a red dot is perfect IMO
i have had a couple 7.5’s lol that is too short and waaaay to concussive hah
I have seen evidence that this is true. 11.5 is what I prefer between the two.
I picked up these two uppers.
I prefer the 11.5" for a variety of reasons. I like the flash can (sound forward muzzle device) that comes with lots of the 10.5" uppers, and I REALLY like the rail that comes with this particular 10.5".
I swapped the rails on these two. The barrel nuts are ALMOST the same. About 15 thousandths difference, so I had to swap them out, too. (By the way, this is not difficult, but I don’t recommend that you do this unless you have the right tools including a vise block and a torque wrench.)
Adding the flash can, swapping the handguards, and adding appropriate grips and braces to the lowers now result in me having an 11.5" that is a little bit more “beefy”, and a 10.5" which is more minimalistic.
I’ll add, that the physical size difference between a 10.5" and an 11.5" is almost not noticeable. The muzzle device choice can sometimes make a bigger difference when it comes to overall length.
However, from a laws of physics standpoint, that one inch can make a huge difference.
The dwell time (distance) after the gas block on a carbine-length gas system is about 3" for the 10.5" and 4" for the 11.5". So, 33% more dwell time is substantial. Whether is provides me with greater functional reliability, I cannot yet say.
The shorter you get, the bigger the ballistic effect on the cartridge.
11.5 is the shortest i would go, preferring 12.5
That being said, I own neither and 14.5 is the shortest i have. I’ve taken CQB classes before (protip: Everyone sucks at it). My main point is no matter what you’re doing with a rifle, ballistics matter. It’s very unlikely you would ever find yourself in a situation where a shorter rifle is a necessity.
I think the sweet spot is 14.5-18".
I think you can make arguments for 20" and 12.5"
Don’t see any point above or below those lengths.
Since the thread was resurrected already, I’ll chime in. As the dead horse has been sufficiently bludgeoned on the ballistics side of it, I’ll stick to completely unscientific anecdotal findings.
I had a 12.5 sbr in 5.56 for a very long time. Was my first NFA experience and is still in the trust, just in the possession of a different trustee. Spikes lower, bcm kino upper that was swapped for an 8" 300blk when i wanted quieter. It was great and did just fine at the ranges we plinked at, maybe out to 200.
Only ever defended anyone when my wife cornered and wounded a nutria wih her .40sw. It chose fight over flight. 12.5" is adequate barrel length at 20yds. The rifle itself was very comfortable and handy. Zero function issues that werent my own fault.
These days, my only short barrels are a proper mpx 8" 9mm, which is more than enough barrel for that, and a 10.5" KS47, which isn’t nearly as impacted by the reduction in length. For 5.56/223, I stick to 16" PSA kits and a lightweight “one gun” I slapped a pencil barrel on that keeps the entire rifle, with optics and a loaded 30rd pmag under 7lbs. My use cases just dont justify the paperwork of a stamp or the discomfort of a booboo brace. I tolerate it on the KS for now, but time will tell.
