I used to shoot those bullets on elk. The first year I hunted ML elk, I dropped a large bodied bull in its tracks with one shot I figured, "hey, this is great, I like these bullets". In the years to come after that, using the same load, I lost a couple of bulls. On another year, I had a bull come out of the brush at 98 yards and stand broadside. I hit him good, and he just stood there. I continued to put powerbelts into him as he just stood there. Finally, on my 7th, and last speed loader, he went down. I was astounded that he stood there and sucked up 7 shots. I recovered all 7 of the bullets, or at least pieces. I determined that the powerbelts are just too soft for elk. They flatten and fragment, so you don't get good penetration because the kinetic energy isn't there. Take this with a grain of salt, as this is my experience. Others here have had success with PBs. Like I said, I had success, but the failures outweigh my personal successes. I now shoot the solid copper 250 grain Thor bullets, either polymer tipped or hollow points. Either style shoots the exact same out of my Knight Ultra Light, and I've had great success on elk.
