Guys,

Just got a chance to slug the bore and take a chamber cast of my new H&H .450 BPE double. Initial measurements for groove diameter are .465 in front of chambers tapering to .454 near the muzzles. Having never loaded for a tapered bore before, what types of bullets and at what diameter are you guys using?

Being .454 at the muzzle, I’m hesitant to run any jacketed 458 bullets through it, but maybe the long easy taper would keep pressures down?

Any help on this topic would be great!

I had an Alex Henry 450 once, with Damascus barrels. I shot .459 1-20 lead grooved bullets in it without issue. I never slugged the bore.

Your Holland is probably from the time when they touted their grease groove bullets.
They were early adopters of greased bullets over paper patched bullets.
Your bullet diameter will depend on whether yo plan on using black powder or a smokeless load and also what bullets your fired brass will allow.

I have a Holland 450 with Alex Henry rifling, shoots best with a paper patched lead bullet. I use a 300 grain bullet patched to .467.

Thanks all for the input. I’m planning on using N for B loads to start, but if results are poor, I don’t have any issues going to straight black powder loads.

size to the throats.
the barrel will do the rest.

Unless you are using black powder; many 19th Century BP cartridges used bore diameter bullets, and the impulse from the black powder obturated them to groove diameter.

many of the later ones used bore diameter paper patched pure bullets and let the B/P do it's job.
most factory's didn't use but maybe half that much tin, 40 and 50 to 1 were the most common alloys used by both Winchester and remington well into the mid 1900's.