Seemingly at random, the overall length of cartridges varies after the bullet seating step. For example, loading 9mm Luger with 115gr Win FMJ into once-fired brass, and adjusting the seating die to give an overall length of 1.120 with no crimp. Two out of three end up at 1.120 or 1.121, but the third may come in at 1.126 or 1.124 and occasionally one may push to 1.116. I'm using an RCBS Rockchucker and a Hornady Precision Seating Die. I've measured with two different calipers, one digital, one dial. I have a similar problem with .380 ACP but not with .45 ACP. Could the actual nose shape of the smaller bullets be inconsistent enough to cause a deeper or shallower push into the casing? Am I doing something wrong? Any advice?