I am sure neck sizing would work tell it wont sometime that is not to your liking, I like your idea of just bumping the shoulder back A bit, I FL size everything shot in lever guns. It wears out brass faster but it always works, 30-30 brass is all over the place. I have had good luck with CFE223 and Leverevolution in the 30-30 both meter well,I would like to hear how they do in the IMP.
