I built an AR last summer and Ive been having an issue, Everything functions fine for the first 50 rounds or so and then a case that looks to be chambered wont fire. I pull it and manually chamber 1 and it shoots fine but the follow up will not, on and on. Every time I bring it to the range its the same. I have tried swapping uppers to see if it was the upper or lower, It is definitely the lower. I have tried adding more lube. After the first time I went over the build and found the spring for the safety detent was crimped from when the grip was installed, I fixed this and still. What should I check next?

The build is a seekins receiver
Jp roller trigger
jp silent capture with tungsten weights( i picked up and installed lower weights no difference)
Jp build kit

Try tightening or loosening the mag release screw, 1 turn at a time.  I’ve seen this be the culprit before.  Start by tightening it, see if that magnifies the problem, if so go the other way.

THANK YOU. I will give this a shot and try it out tommorrow.

Have you opened the action when this happens to make sure the hammer is in the right position? I'd be wondering if the hammer is resetting and falling appropriately. If what you are describing is a weapon that is fully in battery and not firing, and you know it is in the lower, the trigger is the first obvious potential problem. At the same time, I would carefully inspect the firing pin and the brass... are the FTF cartridges showing signs of light strikes?