At this point, they have all been 55 grain. both in 556 and 223 I ordered some 5.56 - 75 grain Hornady (1 box based on the ratings and price on line.) and some 77 gr. Fiocci matchking hollow point to try. Will probably order some Magtec and/or MK262, if that doesn't work.What is the heaviest bullet you’ve used in your box ammo testing?