Adjustable gas tune/velocity discovery

[GaryM]

I was doing more function test on my AR yesterday. Even though it was cycling just fine it wouldn't lock back the bolt on the last round. I opened up the gas tube (ArmeForte, from 3/4 turns to 1 1/2 turns) and found it did lock back just fine. I then took over to the chrony and found my muzzle velocity had dropped from averaging 1020-1050 all the way down into the 970 range.
I had no idea the gas system used that much energy.
Another thing I ran across a few weeks back was how the trigger group can drastically affect cycling. I found that a reduced power trigger spring can fix some of those short cycling problems. I guess the energy needed to pushthe hammer back down is more important than I had thought.
Anyway, just thought you guys might like to know.

BTW, the rifle in these tests is as follows;
16" ER Shaw barrel, trigger group is a Bill Springfield modified factory group. Rifle length buffer with cut down recoil spring.
Ammo is 200gr hardcast gc over 10.3grs of WC680.

[abyssdncr]

Interesting report. I'll definitely be checking this out myself when I get my 8" upper together.

With the armforte tube, you have a carbine length gas system on the 16" barrel right. Looks like we might have to work up separate subsonic loads for gas-operated vs. manually cycled...?

I wonder how much difference in bore friction there is between your gas checked slugs and the heavy Sierras?

[GaryM]

Yup, 16" barrel w/carbine length gas system.
As for the big Sierra and my gas checks I can imagine those Sierras have a hell of a lot more resistance.
I am hoping to try some of them out before too long.