Originally Posted by rewinder
Purchase a 300 Weatherby FL die and a shell holder. Grind down the shell holder .005 to .010. It sizes the brass without touching the shoulders. Sizes all the way down to the belt. I use a 300 Win Mag to reduce the swelling on my 7 mag belts. Cost $40.
I first heard of such practice decades ago. I tried it with my .30-.338 cases with a borrowed .300 Wby Mag die. Didn't work.
The reason was the radiused edge of the die's belt clearance to the body was too great. The ridge in front of the fired case belt didn't get sized back down to virtual new case dimension all the way to the belt. When the die was set to size all the way to the belt, the belt's front edge got sized down a bit and I didn't like that.
After asking a few folks about this, their advice was to cut the middle out of a standard 30 caliber full length die having the same body taper as a .338 Win Mag then grind its bottom square with only a tiny radius on the edge. This let the die be set in the press so it would just barely touch the fired case belt with the ram at its top sizing the case body all the way to the belt; not a few thousandths in front of it.