If it's a .25 huben, mine was most accurate when using .254 diameter flatbase 44-48 grain slugs from AVS. I am currently having Corbin make me a die to replicate them. I tested the .253 zan slugs and the avs were better. I actually ordered a die already in .254 but I had the o-give too round and I can't insert them by hand if I make them the length I'd like to make them. I'm about to list it for sale. It would work for anyone who has a Corbin s press and a newer .25 huben, as long as you make only 40 grain or less with it, or don't mind pushing the slugs in with a tool if you make them bigger