Some interesting numbers...300BO AR

[Dolomite_supafly]

So I decided to see how the gas system of an AR would affect velocity. My AR in 300 Blackout has a 16" barrel with a pistol length gas system. I have the ability to turn the gas off so I decided to check what difference there would be in velocity between "ON" and "OFF".

 

GAS ON

LOW=1051

HIGH=1063

AVG=1056

ES=11.54

SD=6.08

 

GAS OFF

LOW=1071

HIGH=1090

AVG=1078

ES=19.3

SD=10.44

 

So there is approximately 15 fps more, on average, when the gas is turned off. What is really surprizing for me is the ES and the SD were both lower with the GAS ON. This tells me that the gas system is a bit more forgiving  and probably reducing the high numbers some because there is only 12fps between the high and low with the gas on. While with the GAS OFF the difference is 19 fps.

[Romad7]

What does the action do with gas? Does it affect accuracy at all with the gas off?

Edit: I meant what does the action do without gas. Edited May 10, 2013 by Romad7

[atlas3025]

On a dirent inpingement gun, like a standard ar, the gas flows from the barrel, through the gas block and tube, and into the bolt carrier where it pushes the carrier rearward, which ejects the spent cartridge.  Excess gas is vented through the side of the bolt carrier through the small holes that can be seen through the ejection port. 

[Romad7]

Ahhh, I meant without gas. Damn typos!

Good explanation though:-)

[atlas3025]

Ahhh, I meant without gas. Damn typos!

Good explanation though:-)

 

Lol, that makes the answer easier...without the gas supply the action doesn't move at all.  I suspect the gun would be a little more accurate (perhaps imperceptibly so),

[Romad7]

That's what I was wondering. Could be a cool thing with a suppressor (to reduce some of the noise) or when wanting to keep brass from flying away, more like a bolt action.

Fun test though, I guess there is a little more retained pressure with the gas off. I wonder how much for velocity gain you would get with a longer barrel. I know longer barrels usually increase velocity so I guess I'm wondering what length barrel would make the most gains with the gas turned off. Edited May 10, 2013 by Romad7

[Dolomite_supafly]

These are subsonic handloads and hardly close to max pressures.

[BigK]

These are subsonic handloads and hardly close to max pressures.

With velocities just over 1000fps, I was going to ask if used any powder at all, LOL.

[Dolomite_supafly]

It is a very miserly caliber. I can load 875 subsonic round per pound of powder. The cost works out to 4.4 cents per loaded round because I cast as well.

I can load 430 supersonic rounds per pound or 7.3 cents a loaded round.

It gets the same energy as a 5.56 for 1/3 less powder. That is why I LOVE this caliber and embraced it in full retard mode.

[RED333]

Good info Dolomite, have you shot any a over 100 yards, 200 or 300 yards?

[Dolomite_supafly]

I have shot to 150 yards. I am in the process of building a Savage Striker in 300 Blackout.

[RED333]

What kind of drop did it have, in inches?

[GoneBallistic]

I think we need a dedicated 300 Blackout topic.

[Dolomite_supafly]

I think it is something like 15 inches at 150 yards.

[RED333]

I think it is something like 15 inches at 150 yards.

WOW, that is a lot, but I know you are loading for slow speed.