75 grain 5.56 Superformance

[WoodlandShooter]

Picked up a box the other day to try out in my beater carbine to see if it could work in my recce once I got it together.

Well, my "beta" test went well!!

Test rifle upper specs:

RRA Heavy Barrel 16" Carbine gas system, Wylde chamber
Adams Arms Piston system with Adams Arms Monolythic Bolt Carrier

Lower Specs:

RRA Lower
Rifle length buffer and tube

First off, I ran a full mag of good old XM193 thru it.

The loaded up 5 of the Hornady Superformance in it.

Dialed the piston down to 1/3 gas.

Fired two. Primers look good!!

Dialed up to full gas.

Fired three, primers look good, very small (really small) shinny ejector mark.

So, I think with a 16" barrel and mid length gas, with a rifle length tube/Buffer/spring combo, it will work!!!

Next, I need to chrono these bullets, and once the new rifle in done, will need to test grouping.

If I can get 2700-2750 out of these in a 16" barrel, WOO HOO...even better if I can get them to group.

[superdown]

What twist is your barrel?

[Biggerhammer]

I was wondering the same and if it was a function test only or if it was fired for group/accuracy. I had to turn the gas all the way down almost on my Sig 716 .308 with Hornady Superformance so that it didn't beat the crap out of the bolt carrier group and the brass but when I fired it for groups, it SUCKED!

[WoodlandShooter]

It was only a function test.

this particular upper is a 1/9 twist. I dont expect it to be able to stabilize the 75 grain Hornady Bullet.

The rifle I am building is a 1/8 so it should be able to stabilize 77's and 75's

[WoodlandShooter]

Chrono'd them this weekend.

First shot with gas turned off: 2703

two shots with gas at 1/3: 2689, 2691

Last shot with full gas: 2682


seems to run like a Mk262 clone when fired from a carbine.

will test for group once the new barrel arrives.

[Blacklab]

Very cool my next build will be a 223 wylde thinking of going 20 inch.

[WoodlandShooter]

that could get you another 50 FPS...possibly more