All, I am relatively new to this forum and to reloading. I have been reloading .40 S&W for my range consumption and began casting boolits this past fall, starting with Lee and jumping to a beautiful MP that casts 160 to 175 grain flat or HP at .402 inches. I shoot an S&W Shield that, as near as I can measure with the offset rifling, slugs to a width of ~.400 (I have gotten .399 to .400 but I can't get a good angle with standard calipers). I have a Lee push through sizer that consistently sizes to .401. I was casting 175 grain using a Lee mold and Lyman #2 that was casting on the smallish side at .400 or .401. Some didn't seem to even brush the sides of the sizer. I was shooting either PC coated or lubed but was getting some keyholing which I think was a combo of Lyman #2 and undersized bullets.
Fast forward to the MP Mould which casts a perfect .402. I have the option of sizing these to .401 and then applying PC for an end result of about .402 to .4025 or not resizing for and .402 w/o PC and about .4035 after PC. I am casting using 20 to 1 lead. The bullet weighs in at 165 gr and I am probably going with a light to mid load of 231.