plmeek
40 Cal.
Both Rice and Colerain "B" weight barrels have a 1" breech and should accommodate a 3/4-16 breech plug, so I don't see any problem with a .54 caliber at the breech. The waist of both the Rice and Colerain "Golden Age/Classic American" "B" weight barrels is 0.75". That is getting a little thin if the bore is 0.54". You will want to be very careful when installing any underlug in that region and make the dovetails no deeper than say 0.030". That should be plenty strong to hold the wood to the barrel, which is all the lugs and pins are doing out there.
Most of us old farts really appreciate a lighter rifle since we typically don't have the upper body strength we had when we were your age. I think you will like the lighter rifle when hunting. I also think you made a good selection in type of rifle based on your original criteria. The 1-9/16″ wide butt plate and the late trigger guard are suitable for many of the Pennsylvania flint rifles made in the first quarter of the 19th century. The Lancaster stock architecture was very popular and rifles of that type found their way everywhere.
Most of us old farts really appreciate a lighter rifle since we typically don't have the upper body strength we had when we were your age. I think you will like the lighter rifle when hunting. I also think you made a good selection in type of rifle based on your original criteria. The 1-9/16″ wide butt plate and the late trigger guard are suitable for many of the Pennsylvania flint rifles made in the first quarter of the 19th century. The Lancaster stock architecture was very popular and rifles of that type found their way everywhere.