I've recently been experimenting with different loadouts of different rounds in my 9mm mags, i.e. staggering different HPs and FMJ etc. Currently I have 10 FMJ on the bottom and the first 7 or 8 rounds, depending on mag size, are HPs. My reasoning behind this is once the first bunch of shots are fired, cover is usually taken, then the FMJ rounds come into play to penetrate cover. I know some HPs have good barrier penetration but you never know what might stop it. My carry 9mm is all 147gr.