Fat_46 said:
Is there any other way to determine what size 45 cal projectile I need?
One barrel maker said that the last few inches of the bore are the most important for good accuracy. That would seem to suggest that the muzzle measurement where the projectile is exiting and being loaded is the most critical measurement, especially when it comes to ease of loading.
If a good measurement can be obtained from the crown that could be most helpful. Modern bores are pretty uniform if they're not worn much, and a sandwich of wads or an over powder card can seal the gases off if the projectile is loose in the breech after being loaded.
Also, a very light powder charge of about 5 grains or less should be able to expel the projectile into a soft medium without distorting the bullet so that measurements can be taken.
Removing the breechplug can be considered to be an extreme measure with some guns just for the sake of slugging the bore.
Depending on which Buffalo Bullets were tried, some measure .451, or measure one which will help to at least establish a reference point.
Another idea would be to try wrapping teflon tape around the projectile as one would with paper patching. It is a lot thinner than paper.
TC sells teflon tape to wrap breech plugs with and discount stores sell different thicknesses of teflon tape. It's inert and shouldn't burn or harm the bore.
Also, projectiles can be sandwiched in the bore between wads or overpowder cards to hold them in place. While doing that may not produce the best accuracy, one might be surprised to see that the target can be hit relatively close to the point of aim at a moderate distance.
And saboted bullets may also be a consideration.
Trying these methods and determining the rate of twist could help to determine if your gun has the potential to shoot conicals well enough for you at all before going through a lot of hassle only to find out otherwise.