Ran a rig for the first time today. Had 3 light primer strikes,always the first out of a mag. They fired fine later when I loaded them. Bolt not locking back on last round each time. GM20 barrel with factory extension. Buffer Olympic arms pneumatic buffer. BCG toolcraft phosphate 158. Please advise thanks

As for light strikes, what trigger setup are you running?

The not locking back part could have to do with pneumatic buffer. Try a standard buffer and see if that helps.

will do on the buffer,I will switch it out for a standard rifle buffer. Its a Larue MBT.

it definitely slams home harder now. I will do a test for short stroking asap.I wonder if the bolt was not locking fully in the wilde chamber?(regarding the light strikes)  Input appreciated.

We often times over look the buffer. After this last build I won't ever do that again. Long story short. I built an A2 clone from a bunch of parts I scrounged for and took it to my friends farm/private 900 yd range to test fire and zero it.

Zero the rifle. Start shooting mags thru it and it was having all kinds of problems. Partial feeds 3-4 times per mag of 20 rds and no last round lock back. After rechecking everything and making sure I actually didn't put something in wrong, nope everything together correctly. About that time I remembered that I had used this lower and on a midlength/fixed stock experiment I had done a couple of years ago and while it fed fine it wouldn't lock back on the last shot either.  My friend just happens to have many ARs, and also loves full stocks the best so I ask if he has a different buffer and spring I can try to see if it works better. He digs out an A4 style that he never liked much since it wasn't as accurate as he liked (he's an accuracy fanatic). He hands me the parts and all the problems cease. Rifle now runs like a champ and is shooting real accurate too. Well, he takes my old buffer and spring and puts it in his A4 and proceeds to shoot his 100 yard target board and the groups from it went from his documented 1.5" groups to .75" groups.

He then suggested that this trade be permanent, and I agreed.

Damnedest thing I ever saw.

How light??
There is light and there is barely dinged by the floating firing pin when the round chambers.
Barely dinged likely means the bolt was not closed.
Several things can cause short stoking, but in this case the buffer is the obvious place to start.

I would say barely dinged. I wont get a chance to test the new buffer until Thursday or Friday.

If you are running an o-ring on the extractor take it off.
20” rifles don’t need them.
It is also not unusual to see a new weapon need a lot lube on the BCG until it is broken in.

I will check for the o ring and run some extra lube

90 rounds today ran perfcet with the traditional buffer!

I have three MBT triggers and use the heavier spring (supplied with the trigger from LaRue).  I have not had any light strikes.  You might try the heavier spring for reliability.