Nitro450exp,
Here is my two cwents worth. I have done a couple of conversion to 20 gauge rifled. I cut the chambers for three inch shells just as you are going to do, but I found that the 2 3/4 inchers gave me everything I needed ballisticly and are more accurate. I use handcast Lyman hourglass shaped slugs in AA shot wads and cases. I have tried both types of crimps, the rolled ones looked neater but I have had a problem with the very front of the loaded shells being a little too tight to go in easily. I think it is because I shortened the cases before loading by cutting off most of the old folded crimp. If I had a tool to scive the case mouths a little thinner, then I don't think I would have this problem. After trying both, I found that the folded crimps shoot at least as well as the roll crimped ones. Bob H.