Hello all, looking for a little help with my new 6X45 build. This has a 14.5" McGowan !:9 barrel with mid length gas, a Wilson low profile gas block, carbine buffer and spring.

My first test fire was with a 65gr Berger fb. the load was 24.5gr Tac; only one round in magazine to check lock back. This round did not eject the round or lock back. I thought OK, under gassed, I'll check the gas block alignment. Sure enough it was mis-aligned, and I re installed it taking care to get it aligned correctly.

Next test fire, same bullet and load ejected the brass and locked back. I thought great, I'll fire a few to sight in. Well, I fired 5 more rounds and none locked back but did eject the brass, I don't know how forcefully because I used a brass catcher but I don't think they would have gone any distance.

It looks like it is still under gassed, and my only thought is that the gas port in the barrel might be too small? Even if it is, could I cure the problem with a lighter buffer or spring? I would drill only as a last resort. The load I used for testing I think was sufficient, I've used it in other AR's with no problem, in this gun it produced 2380 fps. Could upping the load solve this?

Thanks everyone
JB

I think to start out, I will work the load up in small increments watching for pressure signs and see if this issue doesn't go away. More velocity will be useful on targets and game. I also have an older 18" 6X45 I haven't shot in a couple years. I looked back in my records and saw that I had used as much as 27gr Tac with a 65gr Gentner Blackbird. I did not recall that (senior moment).
JB

Try a lighter spring and see what happens..........I'm using a reduced power spring in a 300 blackout build........with no issues.........I've opened up a few gas ports too..........stick a cleaning rod in the bore and always use a new, high quality drill bit.........not the harbor freight stuff ..........

Update:
I know it’s been a while but time has been scarce lately.
I tried hotter loads and the bolt will still not lock back.
I can shoot several rounds and all is well. Ejection about 3:00, normal distance.
Sometimes first round doesn’t pick up.
Mag I’m using works fine in another AR.
The buffer is a 3oz and the gas system is mid length with carbine spring and buffer tube.

I am reluctant to use a lighter spring or buffer since ejection is OK.
Could the problem be the magazine release? It fits the upper OK and locks back if I manually pull the bolt back with an empty mag.
Does the mid length system need different spring/ buffer???
Really puzzled here.