Not trying to rip on usmachinegun uppers but they are all but out of spec. We have had three come in for repair and had to be tried and squared. Just to get the bolt to slide in and out? Imho. Mpa does NOT make usmachineguns M10 uppers, I don't know who does? But yes call Lisa Foss at Mpa. Sure she could hook you up. Good luck.
Mine was missing the bearing and the charging handle
Flipped around from day 1
Also jammed up a lot
I sent it to Sam practical solutions and he added a spring and found they used a Mac 9 part in my Mac 10 upper
Bottom line. Buy one from Sam. I paid hundreds more for him to fix mine from the other guy