I bought a Stoner 9mm upper from Midway. Supposed to work with Glock and Colt mags. I installed a Yankee hill 9mm buffer 5.9oz. I have the Stern defense mag block to use Glock mags. If I lower the adapter block down past the regular mag catch it will load,fire, and eject about 80% of the time. The rest of the time the bolt doesn't go all the way into battery. I have also tried the endomag adapters that go in a pmag. Same results.This started on a collapsible stocked lower. I have also tried it on a A2 lower my Beowulf upper is on. Same results doesn't go into battery about 20%of the time. Any ideas what to try next? Maybe a 308 buffer spring ? Kinda running out of ideas.