Making bullets for my 9.3x74R gave me fits. I was losing about 1/3 of my bullets due to gas checks going on crooked. The problem is that 375 gas checks are so much larger than 366 bullets. The solution is to turn a very smooth bevel in the sizer die, so that the gas check is held concentrically when the bullet is started. Any machinist should be able to do this for you.

What brand of lubrisizer are you using?

I can't say enough how good the LBT Blue Soft lube is. If you can get it, it's worth the trouble.