Carry the best ammo you have in your primary and spare mags. If you run out of your best SD ammo, load your next best in your last spare mag or BUG (back-up gun. You do carry a back-up gun, right?)
Do not "Dutch load" (i.e., alternate rounds) in your primary weapon. Make it all consistent with your best ammo. You want to have the use of that first. In your case, if you are carrying 46 rounds, but only have forty best, load whatever you have at the bottom of your last mag. But actually you will need to load more because if you have switched ammo, you need to shoot some of those new rounds to verify good functionality with your gun. (Hey, some guns are picky about ammo). Ideally you should shoot a lot of your new ammo, but...
If you only shoot nine new rounds for functionality, that will leave you with one full mag of second-best ammo.