The 1/48 twist is ideal for shooting something like the Maxi Hunter, which is devastating on deer. It weighs more than the patched round ball and does hit harder. I have started shooting these out of my Hawken and find that they are a better hunting round than the round ball, especially out of the stock barrel.
If you are sure you want to stick with a patched round ball, which will reliably kill a deer if you do your job right, you may want to switch out to a 1/60 or 1/70 twist barrel just because I have found the slower twist to be more accurate with the patched round ball. Your accuracy may be suffering enough to not hit the heart lung area and hitting the shoulder instead. Maybe not if you have shot enough to know exactly where it is hitting. The .50 round ball is enough to kill a deer though.