DoubleD:
I did the slugging of the MH .577-.450 this weekend, from the muzzle using a swaged lead .495 round ball. The ball tapped in and engraved well the rifling. I tapped it through the bore and out the breach with a series of muzzle loading rams with patches on the end. There was constant resistance down the bore, so I would say this rules out the tapered bore.
I failed to count the lands and grooves, but will do this later. The micrometer used is accurate. It has been tested several times with known tolerances. Using the slight pressure and turning the slug to register the highest points, the diameter measures exactly .460.
To me, this seams like a good thing. It brings the bullet selection and availability up from one that would be .462-3 or so. Mine is a sporter (with express sights that also have a ladder sight leaf for long range) from South Africa. I would think that the regulation for the sights would center on the military loadings of the .577-.450. The rifle does shoot close to point of aim with the Ten-X 480 grain loads.
I believe I am going to try some long round nose 480 to 500 grain casts.
Any comments or suggestions of bullet types that have worked best for your loadings?