Peabody contract musket bore query

[flintlocke]

My friends, I need some input. Apparently, I have a Peabody European contract musket, ostensibly in 11.15x58R (.43 Spanish to us ordinary folks). Fine, but a cast and a bore slug would favor a .44-77 Remington/Sharps chamber, but the bore, slugged twice appears to be a whopping .459" right in front of the leade, tapering or choking to .452" ish at the muzzle. Three groove rifling, being what it is, makes measuring fun, my method being: gently forcing my slug into a #1 Morse taper painted in Prussian Blue and measuring the diameter at the point of interference. Any glaring errors in my methodology?
Most authorities agree the original loads were paper patched, .439, 370gr....given the tactics of massed ranks and volley fire you still have to wonder about the .020 thou gap at the leade. So what was the original goal of a tapered bore?
Initial testing with soft greased .456 pistol bullets and barely supersonic charges of Unique indicates the old girl wants to shoot, lands are smooth with pitting in the grooves. My main question is, will I start getting pressure issues with slightly harder bullets, say a 10 or 12 Bhn , for instance a .458" 405gr in that tapered bore? Paul.

[mikeym1a]

I have a Belgium Comblain, about the same age, with a similar cartridge. Using a .435 boolit, and three wraps of 16# paper will give you a wrapped ball of approx .458. The grooves on the Comblain measure .453, so I size to .455. This very much takes up the .020 gap, and is in line with the original loading. BUT , if you want to shoot naked lead, Then properly slug your bore, and size to .001/.002 over groove, with a good lube and have done with it. For me, it is the challange of making the paper patching work. Plus, it polishes the bore. Nice looking gun, by the way. Much prettier than mine! mikey

[John in PA]

Is the chamber diameter at the neck going to allow you to fit that large a bullet in the case and still allow it to chamber? As far as pressure is concerned, the action will certainly stand any pressure increase solely due to bullet diameter. (That's assuming your powder charge is sensible in the first place) Whether the primer will leak due to the relatively large (by modern standards) firing pin diameter is another story entirely, and will most likely be the weak link. They commonly have bores that measure over-spec. If using black powder loads, the .44-77 is a better fit in the chamber usually and the bullet will bump up pretty well. With 10 or so grains Unique, I don't know how much bump you get. I do know that the Peabody's have a pretty good reputation for accuracy with Unique at 1100-1200 FPS or less and a close-fitting bullet. Your's seems rather larger than most i hear of, though. "Crown over V" Prussian proof mark on top of barrel breech?