I've tried a bunch of different bullets on NM elk (mostly cows). I now use a 405 gr. .458 Remington bullet in a black crush rib sabot. The bullet is designed for the .45-70 which is comparable to MZ velocities. The bullet is cheaper than most MZ bullets. Four out of five elk dropped in their tracks. The last one ran about 35 yards. My typical shot on elk is around 220 yards. I've heard of lots of failures with Powerbelts, and I believe most are made for deer. Barnes are good bulelts, but the TMZ didn't kill as quickly as I like. My friends use the Expander MZ, with apparently good results. Another friend used the Bor Lock and was happy with it. Another friend uses Precision Rifle Dead Center 340 gr. with good results. I've used the Hornady FPB as well. They worked, but again, not as quickly as the Remingtons. I use 115 gr. of Triple 7. In my opinion, heavy and slow is better than fast and light for elk. I like a bullet that exits and leaves a blood trail. As said above, shoot what shoots well in your rifle. I develop loads using Black MZ power. $10/lb. at Sportsman's Warehouse. It seems to shoot the same as 777, but 777 seems to pour more consistently. Make sure you know the trajectory at different ranges, or use a ballistic reticle scope. If you are hunting in southern NM, wear lightweight layers of clothing, because you'll be carrying the cold weather stuff after 9 a.m. most days. I hunt in waterproff Merrel mid-high boots unless the weather is really bad. If you're from the flatlands, try to come a day or two early to acclimate to the altitude. Carry and drink lots of water. It is dry here. I carry a 70 oz. Platypus hose bag, and usually drink most of it in a day. Good luck.