Adjustable gas tune/velocity discovery
 

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.

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?

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.