Home Forums Hunting & Shooting AR and Tactical Rifles 300 Black-Out Gas Length? Only carbine or pistol?? Why?

For the 556- longer is better.
With the Blackout carbine or pistol is all that is available. They say midlength won't work at all.

Anybody care to explain plain?

This is my understanding. These things are gas-driven. The 300 BO has a very limited amount of gas due to the very small powder charges being used. So a longer gas system allows the gas to de-pressurize as it stretches out over a longer length of barrel.

For the 5.56, smaller bore, more gas produced by larger powder charge, more forgiving on a longer system. But dwell time can become critical. Too little barrel ahead of the port can allow the gas to escape too quickly creating an "under-gassed" situation.

There's more to it than that I'm sure, but that's my take on the basics of it.

That's a pretty good explanation.

Here are a few factors that require a shorter gas system:
- faster powder
- larger bore
- smaller case capacity/powder charge

The 300 Blk has all of those.

The OP statement that "longer is better" is oversimplified and incorrect, even for 5.56 - in barrels 16" or shorter, you can certainly go too long with the gas system. The whole gun is a system that needs to be balanced right, you can't just push one variable to the extreme.

Agreed. Yondering gave a little more detail on what I was saying. I did alot of reading and studying this stuff before I attempted anything shorter than a 16" barrel in .223/5.56. What I arrived at was that 11.5" was the shortest, fully reliable barrel length to be used with carbine gas. And that if I were to build anything shorter than that barrel length, it would be a 300 BO. Again, this was my determination for my purposes, and others will have their own opinions.

To the original question at hand, it seems to me, from my reading, that in 300 BO, pistol gas is pretty much always GTG, and carbine usually is in a 16"+ barrel, but may prove troublesome.

Glad to get the feedback... just now trying to sort these critters out. What you say confirms the review I found on the Aero website:

http://aeroprecisionusa.com/300-blackout-16-cmv-barrel.html

"I bought this barrel to replace a 16" carbine length barrel. My old barrel would only cycle about half the ammo I fed it. After switching to the AERO barrel, it cycled everything I put through it except for a couple of types of subsonics. It did actually even cycle some types of subs without a suppressor. The use of 4150 steel, the QPQ treatment, and the HP/MPI testing makes this barrel a GREAT value. The pistol gas system functions great, and I love this barrel." (Posted on 5/23/2016)

Just a heads up for you. Ballistic Advantage makes the Aero barrels. They're owned by or partnered with Aero a couple years ago.

Barrels are generally a little less expensive direct from BA. And you can look through their full selection. If they say it has the gas block included, you can call them and have them leave it off. Or just go ahead and use.

I bought their 8.3" Hanson profile premium in 300 BO for my build. I'm using a SLR adjustable gas block and an H3 buffer. It's cycling everything I've fed it so far, subs and supers, at about 5 o'clock. It's a little slow. Gonna try adding gas, and if need be switch to a lighter buffer to get it to 3 o'clock ejection.

http://ballisticadvantage.com/8-3-inch-300-blackout-hanson-pistol-ss-premium-barrel.html