RK,

That’s what I did. CPA sent a bullet (with the rifle) that they seated in my rifle, the Mos product that they offer. I took dimensions from it and the throat dimensions that CPA gave me. That info was given to Accurate to make the mold. 

I could have bought the Mos mold but it’s a single cavity and I have a Paul Jones single cavity mold for my .40-70 Sharps CSA rifle. That mold works well. I just wanted to have more than one cavity for the CPA .38-55. Accurate did make the mold right where it should be to replicate my starting dimensions.

One key to this effort is the hardness of the alloy. The softer the better for breach seating the bullet. And if the bullet dimensions are on the “large” side, going a bit softer lets some of those dimensions sneak a bit closer to smaller.

Unlike most readers here, this is my only CPA and my first breach seating effort….so lots to learn!

Tom