Flat based 223 bullets in the MBR and Lyman M die

[reubenski]

I did some research before buying a MBR for the 650. Found a lot of folks that had problems keeping a flat based bullet on a case while rotating the shellplate. Most folks said the fix was a Lyman M die. Basically an expander mandrel to open the neck. So I bought one. It expands the neck .003" but still doesn't hold a FB bullet. I started off just lightly belling the mouth and ended up fulling expanding the neck. No dice. Still doesn't hold a Hornady 55gr SP. 

Any ideas?

[reubenski]

ha, just solved it. Thought about deleting the post but figured someone else might need the info one day. 

If you pull the Lyman M die apart, the mandrel and threaded stem are one-piece. At the top of the mandrel, almost where it meets the stem is a slight step in diameter. If you screw the die almost all the way down and then thread the stem very low in the die you can get that larger stepped diameter to make contact with the mouth of the case and it slightly bells the case mouth. The FB bullets will then stay in the neck. It looks kind of ugly and there's no way I'd do it for match ammo but the seater corrects the bell'd mouth and the crimp die negates all the deviation

[xdr]

I'm glad you posted this as I have a Lyman M die on the way for flat base bullets.