300 Blackout vs 5.56 NATO

[The Annoyed Man]

I know you said you wouldn't use it for home defense, but I eventually plan to. Other than its suppressibility, it can be effectively shot out of a 9.5" barrel without too much muzzle blast or percussion.

I once built a 7.5" AR-15 5.56 cal pistol, and it was way too disorienting to shoot at my indoor range. Even with double ear pro, it was LOUD and I could see and feel the muzzle blast. Definitely not something I'd ever want to shoot inside my home.

That's why I plan to go with a 300 Blackout rifle or pistol with a suppressor. Then, I can actually hear if I ever need to use it without ear pro indoors.

I just fired some subsonic ammo out of my suppressed 5.56 carbine on Wednesday, and it was magically quiet. I mean, it made a little "pphht" and that was about it. The problem was that it wouldn't cycle the action, turning it into basically a bolt action, and making it useless for home defense. I'm going to build a .300 upper for it....maybe as an SBR...and suppress it for home defense. I already have the AAC flash hider / suppressor mount for a .308 caliber barrel, and a .30 cal can for it. If I can shoot a .300 Blk suppressed as quietly as I can the 5.56, then I don't have to worry about harming my ears, or my wife's or dog's ears, if something goes bump in the night.

[MeMelYup]

Does your 5.56 have an adjustable gas block? I have heard some people say that makes a difference.

[Rayden]

Thanks. I have two 5.56 lowers back from the days when my brother used to work on that show on the Discovery channel called "Sons of Guns." Got two of their lowers with special serial numbers for me. I am just getting around to contemplate building a 5.56 16" Carbine and something else with the 2nd lower, perhaps a SBR of some sort and that's why I was looking into the 300 BLK.

I am new to ARs ... so you mean with a 5.56 lower I can use it for the 300 ACC too?

Yes. You can even use the same magazines, but be VERY careful to label them as .300Blk so that you don't accidentally try to feed a .300 cartridge into a 5.56 barrel.

[The Annoyed Man]

Does your 5.56 have an adjustable gas block? I have heard some people say that makes a difference.

If that was directed to me, yes, it does. My 5.56 has a mid-length Adam Arms gas piston conversion kit with a 5 position adjustable gas block. It works just fine with suppressed supersonic ammo. I suspect that it is a problem having to do with there not being enough of a gas impulse from a subsonic 5.56 round, even with the gas block turned all the way up, to overcome the combined inertia of the BCG/buffer/buffer spring.

I spoke with a cop friend at church today about it, and he has a suppressed AR too. He bought a .22 LR conversion kit for his, and that cycles just fine with subsonic ammo, being quiet as a mouse.....but it is only throwing a 35 grain bullet compared to my 77 grain OTM.

I saw this yesterday: http://www.tacticallink.com/Taccom-Ultr ... -AR15.html. I sent them an email asking of their lightweight buffer can fix the problem. We'll see....

[DanD]

I'm in the process of building an AR and one thing I noticed is that when the hole in the gas block is aligned with the gas port in the barrel the gas block does not touch the shoulder on the barrel. Had I not measured the location of the gas ports I would not have known they were not aligned when the gas block was seated against the shoulder on the barrel.

If you did not measure for port alignment when you mounted your gas block you might want to do that.

[The Annoyed Man]

I'm in the process of building an AR and one thing I noticed is that when the hole in the gas block is aligned with the gas port in the barrel the gas block does not touch the shoulder on the barrel. Had I not measured the location of the gas ports I would not have known they were not aligned when the gas block was seated against the shoulder on the barrel.

If you did not measure for port alignment when you mounted your gas block you might want to do that.

We did. My gunsmith son mounted the gas block, and I watched him over his shoulder. It was done right. The rifle DOES function normally without the suppressor, and it functions normally with the suppressor if using standard velocity 5.56 ammunition. It is only the 1050 fps 77 gr OTM that doesn't cycle the bolt, and this is a common problem with subsonic 5.56 ammo. It's not the rifle, it's the ammo.

[DanD]

It's got to be nice to have a son that is a gunsmith. To bad it was not a gas port alignment, that would have been easy to fix.

As you had mentioned before, a lighter buffer may help.

Just curious, but would a carbine length gas system produce a bigger gas impulse because there is more barrel between the gas port and the end of the barrel resulting in more time for the gas to do its work?

[SigM4]

As TAM points out subsonic 5.56 ammo is horribly unreliable in a semi auto firearm. Reason being it's a crap shoot trying to make 5.56 subsonic, either with heavy bullets, less/lower powered powder, or any combination thereof. Thus, the 300 BLK caters to the AR-15 crowd that wants to run suppressed with some reliability. As discussed a simple upper swap nets much better results than any "subsonic" 5.56 loading ever will.