That is going to depend on the maker of the Hawkins. The term Hawkins does not in any manner refer to a single gun maker. While Thompson Center, CVA, Traditions, and numerous other companies all make "Hawkins," they are not alike in all things. Just as they may differ in the hardware, they very well vary in the barrel strength used.

Some custom Hawkins, I have read posts of 150 grains of loose powder. Other rifles are technically limited to 100 grain of loose powder and 85 grains of the super loose powders such as Triple Se7en or Black Mag3.

Normally I suggest you keep .50 caliber Hawkins 110 grains or less. Most of the rifles will come in between 80 grains and 100 grains. This of course is dependent on the type of projectile used. It sounds like you have a good load working up there...