450Bushmaster.net

I purchased an upper from Bear Creek Arsenal and had the same issues with it not cycling. I decided to try the simple stuff first and see if I could resolve it w/o having to drill out the gas port. I removed the bottom plate of the Bushmaster magazine and removed what I guess is a lower spacer. Some folks have cut off some the spring, but I thought I would see what happened just removing the spacer. I then used some needle nosed pliers to very slightly open up the first 1/4” of the lips so the round would slightly tip. I loaded a few rounds and compared the angle to another magazine and I could see that the adjustment let the round tip up ever so slightly. I then took a fine stone grinder on my Dremel and polished the lips.
Out to the field for the test and the gun cycled perfectly.