I think it's a great question partly because I've been doing the same research myself recently. I have always had a .45 biased collection. I picked a Glock 9mm a few years ago and have always run 115gr with no issues. About the time I purchased my first FN (FNS9c), I began seeing posts about 124gr and 147gr for quicker break-in (that or racking the slide for hours on end). I found some 124gr and 147gr for roughly the same price as 115gr and launched experiment "fast break-in". As it turns out, the FNS9c loves all three and is very accurate with the 147gr. I'll continue my range research, but at this point am confident with any of the three rounds tested. Happy shooting!