Several to choose from that I consider superior to powerbelts:
Bullshops are great bullets but have to be ordered from Alaska and can't be in a hurry to get them:
http://bullshop.gunloads.com/tbs_products.htm
No excuses makes really good bullets, but you only have one choice in 54 and it is big!
http://www.muzzleloading-bullets.com...es/Page319.htm
430 gr Maxi-balls are good elk medicine too:
http://www.cabelas.com/product/Shoot...3Bcat104547780
425 gr Great plains bullets are good as well:
http://www.cabelas.com/product/Shoot...3Bcat104547780
I have switched to 50 cal because bullet selection is wider (such as Thor barnes bullets and Hornady FPB bullets) Both great elk bullets, but they are not available in 54 cal.
Bullshop and No excuses are both great elk medicine, but Maxi-balls and Great plains are probably easier to get. I would not hesitate to use any of them on elk.
That said, if I were forced to use powerbelts, I would use the 405 copper aerotip. Powerbelts have a name for coming apart on game ,but usually that is from people pushing them too hard. Stay at 100 gr or less on powder and you should be fine. 100 GR OF POWDER IS PLENTY TO KILL ANY ELK WALKING.
My two best elk loads are 90 gr of BH 209 and a 350 gr hornady FPB (50 cal) and 95 gr of BH 209 and a 300 gr Thor (50 cal)
What gun will you be using? I suspect a sidelock? That means you will be restricted to pyrodex or 777 if you don't use real black powder. Anything in 90-110 gr range should work for you, just have to work up your most accurate load.