Hey, I built a new AR15 from parts kit. I got the kit and parts from different places. I put it together and it all seems to work correctly. But when I try it with live ammo, it malfunctions. It seems that when the bolt comes forward and strips off a round from the magazine, the bold turns very slightly as it does this. When it slams shut, the splines of the bolt don't mesh with the slots in the barrel. What causes this? I've polished the feed ramp, I've tried new and different magazines, I've dried different bolts and even whole bolt assemblies and it is always the same... any ideas?