I was having this same problem loading core lokts for my 300 saum. Each core lokts measures different depending on how big a glob of lead is on the tip of each bullet. I just bought some Nosler Partition 180 gr Spitzers and measured their OAL before I even started loading any and even though they were not exact they were far more consistant in OAL than the core lokts and whenI loaded some this evening I had no problems maintaining my OCL almost to the exact.