I made the resize die .3765, to get a cartridge that will chamber. I took a snap gage and measured the inside of the chamber at the front of the neck and the thickness of the brass ,totaled it up and that is what it took to chamber a round in this barrel,with the brass and bullets that I have. The fire formed brass now measures .378 id. in its unsized condition. It will expand up to .379 or .380 easy. I will have have to cast some.379 bullets as I am out now ,and give it a try . 26-t