Weg Welcome to the forum ... You gave us a great photo ! your gas tube is too short for the first problem....you see the half moon...of course you do...the end of the gas tube has to protrude into the upper half way into that half moon...you are a bit short...and yes that makes a difference.
always on the ar 308 you must function check with one round in a mag...charge it ...shoot it...and the bolt catch must hold back the bcg on one round...if not you have problems of course you know that...but one round and then the bcg has to be caught by the bolt catch...99 % of the time if not held back you are undergassed...and with the short gas tube it proves out....make sure your gb is positioned properly and get a longer gas tube ...also you might wanna check the gas port opening and see what diameter it is... Wash
I just wanna make sure that you check to see if the bolt catch holds the bcg back on one round...this is a Must!
also you said aftermarket buttstock....check the inside of the buffer tube with a ruler...7 inches from back of tube to exit
yes you have a rifle length gas tube...but its too short
yes I see the thread bout extractor's.... but you must see if its an under gas problem first
Lane....haha...sometimes I can be faaaast
On a Seekins adj gas block 3 turns out is nothing! A wise man on here once told me to always start the adj, gas block turned all the way out...then you can begin turning the gas down....you are under gassed ...and you must lube your new piece really well cause these 308's when new are very picky...lube and gas it...you are too short on the tube ...open the gas block all the way
did I mention that the bcg must be held back on one round by the bolt catch?....lol