Amazing how people can bicker so much over stuff that doesn't matter. The .243 is semi-improved already. Blown out to AI the shoulder gets a lot steeper and moves forward, which changes body taper, but shoulder diameter hardly changes at all. I've no idea what that does to internal volume. The only thing that matters is what it does to how it shoots. My first 243AI was a rechambered factory 700 varmint barrel. Comparing accuracy loads......as a 243AI it shot 70's at the same speed it shot 60's before as a std. 243......3800fps. That's a good enough improvement to make it worthwhile. I've had a few re-barrels since then. Accurate velocity from a 25 & 26" barrel with 70's is 3855 + or - depending on which bullet/primer, and which gun. That combo works fine on pds or rockchucks at 500yds.
