Bishop Creek:
"***. Once you cut the port, the "non-firearm" cap and ball becomes a legal firearm under
Federal definition. No problem doing it for your own personal use (depending on the state you reside in),(***)."
Depends upon the primary use of the port (if you intend the port for greater ease of use of percussion cap placement, no, it doesn't fall under category of "firearm" in Texas, 'course where you live it's probably different).