Gas system length

[twokitties]

Hi, getting ready to buy my barrel for my 300blkout build. I live in New York so a supressor isn't in my future. I don't think I will be shooting subs either. In Blkout is a carbine gas system like a mid length in 5.56?

[nolwark76]

No. For AR-15 plateforms, carbine is carbine, midlength is midlength. Regardless of caliber. That's the cool thing about the 300 BLK. You could buy a complete AR carbine kit, buy a 300 BLK barrel, sell the .223 barrel and build it. No special parts needed. The only difference in a .223 and 300 BLK rifle is the barrel. Same bolt, magazine, everything but the barrel.

Good luck and post pics in the pic thread when you are done.

[20X11]

Except, you wont find a barrel in mid-length...16" barrels in carbine gas length only

[nolwark76]

Thanks for helping me when I omit the obvious. I'm sure someone out there will build you a mid length but yes, carbine length gas is all you will find.

[Quiet Riot]

Actually, you will find most 300 BLK barrels are pistol gas, including the new 16" barrels from Noveske. Carbine gas doesn't work for barrels shorter than 16", and many are finding that even at the 16" length, pistol gas works better.

No matter, gas tubes are cheap if the barrel you choose doesn't come with one (I think Noveskes do).

[Legionaire]

I would think the pistol length gas system might be better on a 16" if all you shot were subs. If you shoot supers carbine length is perfectly fine for function in fact my 16" is carbine length and it works fine with supers and subs and it does function subs unsuppressed.

[-k-]

Hi, getting ready to buy my barrel for my 300blkout build. I live in New York so a supressor isn't in my future. I don't think I will be shooting subs either. In Blkout is a carbine gas system like a mid length in 5.56?

In 300 BLK the carbine gas system is as long as possible for a 16" barrel, it would be like a 16" 5.56 with a gas system between mid and rifle.

[Klem]

I would think the pistol length gas system might be better on a 16" if all you shot were subs. If you shoot supers carbine length is perfectly fine for function in fact my 16" is carbine length and it works fine with supers and subs and it does function subs unsuppressed.

I agree...that is my experience also with the same settup (16" with carbine gas, 1:8 twist).

To my mind it is a delicate balance between not having enough pressure to cycle properly with subsonics, and having too much pressure/dwell-time with supersonics.

I find the weapon cycles flawlessly with supersonics but there is a very narrow window of subsonic that works. Compounding this is a 1:8 twist, so I cannot use too heavy a projectile or risk it being unstable in flight, and cannot go too light because to keep it subsonic there is then too little pressure to cycle.

What does work subsonic in this rig is a 220 Sierra Pro Hunter RN doing 1010fps. It cycles properly without needing a suppressor - with 12.1gn of AR2207, Seating 56.75mm (as far out as a magazine will allow...to maximise the powder needed, so that it maximises cycling pressure). Jump to lands in a CMMG chamber for this bullet and CAOL is 2mm so it pays to seat long anyway.

I am starting to think that a slightly faster 1:7 twist would make a 16"/carbine system more subsonic-friendly.