ORIGINAL: nksmfamjp
Well, I'm going to simplify this a bit. Deer(and everything else) are killed by the diameter and passthrough. Diameter(expanded, if that applies) is what determines the overall diameter of tissue damaged.
Passthrough is important because of the length of the wound channel, and because exit holes bleed much more than entrance holes.
So, you need to find atouger bullet which will exit. Your bullet is exploding, which causes more damage where it explodes, but it carries a much smaller diameter to it's final resting place. It also causes it to not exit. Lowering your powder charge might help. Pellets will never give ideal results, theye are just easy. They are too coarse. Try loose powder somewhere between 100 and 150 grains. If you lower your charge down, the current bullet might hold together and exit on these close shots. With "quick loaders", you can load as fast as pellets and be more acccurate to boot. Also, you might look for a bullet designed for higher velocities.
Unfortunately I have to cry foul on that statement. While many deer are harvested due to the wound channel and loss of blood that would be a very real scenario for archery. When shooting a deer with a firearm be it a rifle, pistol or muzzleloader the real killing power comes from the hydrostatic shock that is imparted as the bullet strikes and enters the target. Also bullets do not explode, there is no explosive charge in them, bullets fragment, some more than others. Like has been said the powerbelts are not the best choice for powder charges above 100 gr. I personally shoot a CVA Wolf and use 130 gr of pyrodex pellets and WW 209 primers pushing the 250 gr Hornady SST muzzleloader bullet. The T/C shockwave bullet is made by Hornady and is an SST with a yellow tip. I consistantly get 2-3" groups at 100 yds with that bullet/charge using my ghost ring sights. I'd suggest finishing up your season with what you have and during the spring and summer buy some different bullets and see what your gun likes best.