This is cross posted in the Single Shot rifles discussion forum because I forgot there was a separate forum for black powder rifles. My apologies for the double posting.

I'm having a Commercial Swinburn's Patent Martini restored and as part of the restoration process, it is being converted back to centerfire (it had been converted to .22 rimfire). I'd wanted to have it barreled and chambered for .303 (the British .303), but my gunsmith thinks the firing pin setup is not sufficiently strong for a cartridge of that pressure level. He's suggested I stick with a black powder cartridge from the era in which the original rifle was manufactured.

The two cartridges I'm considering are the .450 No. 2 Musket (which appears to be the cartridge for which the rifle was originally built) and the .450-400 BPE. Although I had fantasies of using it as a short range elk rifle, in reality the largest animal it will ever hunt is deer or black bear in the woods of Pennsylvania.

In terms of availability of components and the use for which the rifle will likely be put, would you favor one cartridge over the other? If so, why?

Can you point me toward a source for reloading components for either cartridge that actually has them in stock?

Thanks.

I replied in the single shot section.