Short barrel complete upper 300 blackout

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rabid wombat

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Please let me know your thoughts on complete short barreled 300 blackout uppers. I am fully expecting to shoot only subsonic through a can. Any thoughts and ideas are greatly appreciated.
 
8" with 1:7 twist seems to be the way to go if you are going 300 BLACKOUT.
 
I am also curious about this. Why the 8" over say 10.5"? Obviously, 8" is nicer because it's shorter, but does it cause the rifle to be more probed to malfunctions due to having to run a pistol-length gas system instead of a carbine or rifle length gas system? Also, how much louder is the .300BLK in an 8" barrel in comparison to a 16" or 8"? I've been considering a .300BLK upper in either the 7.5-8.5" or 10.5"? What are some good makes? The Radical Firearms uppers are under $300 and seem to get good reviews but I don't have personal experience.
 
I have an 8.5" and a buddy has a 10.5", both pistol gas systems, and both built as pistols. I can't hear any discernable difference in volume between them, and very little difference in muzzle flash. The 16" i had was just the tiniest bit quieter, but not that much, and it ran a carbine gas system. I built the 8.5" but the other two came complete. Ironically the two pistol uppers are using exactly the same gas block. Might even be the same size gas port too, but i cant be sure. They both shoot well.

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Most .300 blk barrels have a pistol gas setup... even some of the 16"ers.

When I looked into it, the common wisdom was that you aren't gaining anything by going longer than 10.5" on blk subs. Quickload shows my pet sub load (H110 and 240gr SMKs) not gaining appreciable velocity at the 9" mark.

All of that being said, look for 8-10.5", 1 in 7 to 1 in 8, and pistol gas.
 
What can will you be running? Some cans have a minimum barrel length requirement.

I have a 10.5 300 blk and a 7.5 in 223. Both SBR's, built originally as pistols until the stamps were approved.
 
Ranger Roberts said:
What can will you be running? Some cans have a minimum barrel length requirement.
Click to expand...
That doesn't matter with 300 Blackout subs. Even a 9mm can with aluminum baffles can handle 300 Blackout subs.
 
There's really no reason to go with a longer barrel with 300 BO subs. I'd recommend an 8" barrel because it's short and also because it's popular; you'll have no trouble finding rails that butt right up to the back of the can exactly.
 
I have 7" , 8" and 10.5" uppers/complete guns. Not a licks difference in how any of them function. I like the 7" the best.
 
A friend of mine has uppers in 8.5" and 10.5" that he let me shoot when I was planning my build. He thought the 10.5" was more pleasant to shoot but I could not discern any difference. I went with an eight-point-something barrel and am happy with it.


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I built a 300 blackout upper with a 8.5 inch CMMG barrel using an SLR adjustable gas block and a Joe Bob side cocking upper. When running subs with either pistol or centerfire rifle can it is a joy to shut the gas block off and shoot quietly as a straight pull bolt action. Even shooting supersonics in semi auto the side cocking upper reduces gas in face blowback. Plus the SLR adjustable gas block allows for tuning to load or adjusting to blowback from the can crudding up the action.
 
If you are only going to run subs, I'd recommend a 9mm instead. Ammo is much cheaper, hollowpoints designed to expand at subsonic velocity are much cheaper, and ballistics have only minor differences until past 200yds.

The advantage .300 has is being able to also use supersonics much faster than most pistol calibers and a good ballistic coefficient if you want to lob subsonics downrange like mortar rounds.
 
Pay attention to your suppressors minimum barrel length recommendations if you plan to shoot supersonics.

I don't have a .300 BLK yet, mostly because I don't need another caliber to reload for at the moment. But if I build one, it'll be 8.5" to shoot only subsonic through my 9mm suppressor. For .300 BLK full power, I'd rather use 7.62x39 instead in my 10.5" upper with 7.62 can and not bother with .300 BLK as the 9mm can is much lighter than my 7.62 suppressor. This 7.62x39 is a sweet setup despite the "crack" from the supersonic rounds, although it is a bit heavy given the can is rated for .308.

YMMV.
 
Its a LOT cheaper to reload 300 BO than 7.62X39 in both subsonic and supersonic. Brass is just converted 5.56 which you can find anywhere, bullets are standard 30 cal .308 and much easier/cheaper to find in light and heavy weights than the .311 based bullets. Ive got components and shells to do 5000+ rounds of 300 BO . I couldnt afford to do that with X39. With the upcoming post election ammo shortages make it easy on yourself and get the stuff thats easiest to get.
 
Sorry to steal this thread, honestly I am.
What was your point of impact shift POI with those cans. I intend to do supersonic and subsonic loads. But, above all I I care about accuracy, sound reduction, finally price.

How happy are with the cans? Is there anything you wish you could change. I was looking hard at the omega, but barrel is kind of long 308/300 BO. This will share a home on my AR10.
 
Slight shift with the Specwar to the upper left. 1 MOA or so. No perceptible shift with the SIG can.
 
I used an 8.5" barrel. That was mostly because I have a suppressor and wanted to stay shorter than my 16" 5.56 AR.
 
I was wrong about the minimal barrel length for the Omega in

300 BO it is 8 in
16 in with 308/ 7.62x51

http://www.silencershop.com/silencerco-omega-7-62.html

Anyone have experience with these as well?

How does it compare with the Sig 7.62 TI. I know it is light and quite than the Specwar.

Also how the hell can i make the font bigger from my phone?
 
Last edited:
TexasEric said:
Seems like the Omega is lighter, quieter, but slightly pricier.
Click to expand...
You shouldn't go by manufacturer numbers when looking at dB levels on a silencer. And even 3rd-party tests have enough different variables that the same can will often have very different dB numbers in different tests. By far the best way to determine which silencer is quieter is to look at comparison tests.
 
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