I have had several 54 cal 1:48 Thompson center barrels. I have never had one that would not shoot a PRB good enough to hunt with. Actually all have shot really well. All of mine have liked a .530" or .535" ball with a .015" or .020" patch with around 90-100 grains of FFG. I have never had a 1:48 T/C that would not shoot a PRB with great accuracy and I have had them all from .45 cal to .58 cal. Play around with ball diameters, patch thickness, and powder charges and you will find what you are looking for. Also with the shallow groove with the T/C barrels I have found that depending on the barrel you may have to clean after every shot to every 4-5 shots. All barrels are different.