Wish I could help out with suggestions, but I have no idea why the BCA uppers would cause the bullets to pull and the Hardened Arms upper does not.
If anything, I would have expected the rougher feed ramps on the BCA's to cause set back of the bullets instead of bullets slipping forward in the neck.
I tried the Hardened Arms upper first with a single-loaded mag and I thought "no way, it didn't move!" and that is when I made up two more dummy rounds and really racked the charging handle all the way back and was even pointing the barrel downward while letting the bcg slam the dummy round home. Ran through the three and no movement, so I ran them all through again and again. Still no bullet slippage.
My final test was on the bench to let the gas system chamber one and to clear it and check the measurement. I am good to go!! And again, this was with NO crimp at all. Just neck tension from the standard New Dimension Hornady die set.
My 5.56 and also the .300 BLK neither one cause any change in OAL.
Just puzzles me.
If anything, I would have expected the rougher feed ramps on the BCA's to cause set back of the bullets instead of bullets slipping forward in the neck.
I tried the Hardened Arms upper first with a single-loaded mag and I thought "no way, it didn't move!" and that is when I made up two more dummy rounds and really racked the charging handle all the way back and was even pointing the barrel downward while letting the bcg slam the dummy round home. Ran through the three and no movement, so I ran them all through again and again. Still no bullet slippage.
My final test was on the bench to let the gas system chamber one and to clear it and check the measurement. I am good to go!! And again, this was with NO crimp at all. Just neck tension from the standard New Dimension Hornady die set.
My 5.56 and also the .300 BLK neither one cause any change in OAL.
Just puzzles me.