Thanks for the help guys! After some experimenting, I ended up with an OAL of 1.221" any longer and the "shoulder" got a little too high. I put 100 rounds through my 5" Kimber yesterday, and it functioned 100%. Also very accurate! Beats factory ammo all over the place. Not to mention those beautiful clean holes in the paper
For powder, I'm using 5 grns. of Winchester 231.