Found this on Powerbelts website:

Q. What's the best grain weight for deer size game?
A. This question has been debated as long as hunters have been going into the woods to recreationally hunt. Most people agree that a heavier bullet provides more energy and affords a quicker cleaner kill. The trend in muzzleloading has leaned towards lighter faster bullets for longer range shooting. It is important that you match the bullet to the rifle for optimum performance and that you choose a bullet that will provide enough energy on the game that you are hunting and out to the ranges you are expecting to shoot that game.



Q. Is muzzle velocity the only thing to consider when choosing a bullet?
A. Whereas velocity can help make shot placement easier at unknown ranges, terminal bullet performance is the most important aspect of choosing a bullet. PowerBelt Bullets are made of pure lead and will expand uniformly on impact. This is very important to the efficiency of energy dispersion to the target. If a projectile exits the far side of the target animal and continues downrange it is carrying energy with it that could have been displaced in the target animal.