While setting up my new RCBS 10mm dies (carbide 3-die set), the instructions said to set the crimp as follows: After seating a bullet, measure the case just about .25" from the mouth of the case (not all the way at the top, but about where the base of the bullet is inside the case). Then, measure the case right at the mouth (very top of the case), it should be equal to or slightly less than the diameter of the first measurement. Well, I have mine set so that my two measurements are .421" at base of bullet, and .4215" at the case mouth. This is basically equivalent (as per the instructions), and I tried turning or pushing the bullet back into the case, but it feels very secure. I'm just thinking that maybe I should crimp it a little more. I'm more worried about developing sufficient pressure to achieve complete combustion, as set-back seems to be a non-issue. I've measured bullets after cycling them several times vigorously, with no set-back. What do you guys think?