Posted this in Tony's thread, but didn't want to drift it to far from his topic

I've been thinking about a 300BO AR pistol for a few years, put on hold with the whole pistol brace shenanigans.

What's considered the 'optimal' barrel length for a 300BO that'll primarily be used suppressed with subsonics?
Years ago, I thought I'd read something about a length in the 10-10.5" range was 'ideal' but that gets you nearly back to 16" rifle length with the can on the end.

PSA had some good deals on complete braced pistols, has me thinking about it again.
This one in particular caught my eye, but they also have options in 7, 7.5 & 8.5 inch models
https://palmettostatearmory.co...stol-5165448816.html

Edit: Looks like those daily deals are all now OOS, but still may proceed without going to complete build route

You might try to find velocity and energy figures for the ammunition you’re considering using when fired from short barrels.

Without doing any research myself, though, I suspect that a few inches here or there would have no significant effect on the terminal ballistics of most subsonic loads.

With subsonic loads, a weapon chambered for 300 Blackout is just an oversized handgun, and a subsonic bullet in the ±190-220 grain range will act like any handgun bullet, albeit being smaller in diameter than most and perhaps not expanding as well due to bullet construction. In addition to being handier, a really short barrel might help ensure that all subsonic loads really remain subsonic.

If, however, you are planning to shoot at longer ranges and want the best ballistics possible for the purpose, then it might do to choose a barrel that produces the muzzle velocity that is as close to maximum subsonic without going over as possible.

Added:
In my own limited testing of the Hornady 190 grain subsonic load, from a 16+ inch barrel its average MV was 1056 fps; from a 9 inch barrel it was 1041 fps, or essentially no difference. The extreme velocity spreads of the tests actually overlapped so that some shots from the 16" barrel were slower than some from the 9" barrel.

Wasn’t the original intent for 300blk to burn all its powder in 9” of barrel (for subsonic)?
Wouldn’t that make anything past that length kinda moot?
FWIW, I have an 11” 300blk that does quite well with my Octane45HD (I do not run SuperSonics through it as it is not rated for those pressures)

From what I remember reading the optimal length was 9” as it allowed full powder burn. I imagine anything between 8-10” is probably pretty similar but ya going any longer is probably just adding weight and unnecessary length. I haven’t looked into it in awhile, but I remember deciding on a 9” for my AR pistol but I can’t suppress in CA, so idk if that changes things at all.

quote:

Originally posted by hudr:
Wasn’t the original intent for 300blk to burn all its powder in 9” of barrel (for subsonic)?

I don’t know anything about the original intent of the cartridge design, but based on the example I cited above, that could be true. FWIW, the factory short barrel of the SIG 300 BLK MCX Virtus barrel is 9".

For a few more examples of subsonic muzzle velocities from a 16+" barrel (very few rounds of each fired):

American Eagle 220 grain OTM: 1038 fps
Nosler 220 grain OTM: 1035 fps
Hornady 208 grain A-MAX: 1035 fps

On the other hand, for the Hornady 110 grain V-MAX supersonic load, the muzzle velocities varied widely based on barrel length:
9" barrel - 2180 fps
16" barrel - 2389 fps

Thanks gents, now to keep an eye out for a deal.

10.5” pistol hear with a YHM Ti Pantom. Firing 220 gr subs - all you really hear is the action of the firearm.

I’m building an 8.2” when all my Black Friday parts arrive. YHM Resonator 2 in Jail. I’m excited about this one

I scored a complete with BCG aero 8.5 inch 300 upper for $200 a pawn/gun shop. Went home slapped it on my SBR lower screwed on a muzzle device for my 30 cal suppressor and went out to the back yard ( legal to shoot on my size land in my area). 220 subsonic ball ammo and it was quite loud. Only thing I can think of is the muzzzle device was not lock tight or rockset in but hand tightened with a wrench. But that shouldn’t make too much difference. Maybe my suppressor sucks. It’s a rugged micro30

Anyway. 8-10 inch seems ideal for a suppressed 300 per the testing people publish. I looked at various lengths but as noted, I fell upon a 8.5 cheap

I have both a 10.5 pistol and a 16" rifle. Yes, I like how 300blk is optimized for short barrels, so ballistically you do not suffer much in pistol lengths. However I have noticed a noise difference. The rifle is always quieter with subs and suppressor on. Just the last of the powder blast I suppose. Rifle can sound like a (subsonic) pellet gun with subs.

My 300Blk, BCM sbr has either an 8.5” or 9” barrel. I can’t remember