Optimal bullet diameter

[The Double D]

There is a great deal of discussion when it come to the optimal bullet diameter for the 577/450 Martini cartridge and it it's Henry rifling.

Here is a the official description of the British Military Henry rifling:

As issued, Henry's barrel had a nominal bore of 0.450-inch, obtained by allowing an 0.449-inch plug to run, whilst rejecting one of 0.451-inch. This bore was slightly enlarged at the breech end, so that an 0.451-inch plug would run in four inches from the breech, and one of 0.450-inch, eight inches. From this point to the muzzle the bore was cylindrical. The grooves in the tapering section were 0.009-inch deep to within one inch of the true bore, and from there to the muzzle 0.007-inch deep, giving a relieved bore of eight inches, with progressive grooves for seven inches. There were seven grooves of a right hand uniform twist, with one turn in 22 inches. The chamber was cut in the barrel, and was coned 0.018-inch to ease extraction.

Using only to figures given in this official description what should the optimal bullet diameter of a cast lead slug used in this bore be?

[Buckshot]

.................Here's that dastardly word............Depends . Mks I, II, & III were tighter then the MkIV. A grease grooved .465" slug will work in the first 3 marks, or a smaller slug patched to that. The MkIV took a slug of .472" over the paper patch, however it shared similar construction, ie: choked for a distance beyond the chamber mouth.

..............Buckshot

[BruceB]

Just yesterday, I saw a 1979 photo on the Internet , which showed a fairly-elderly and VERY hard-bitten looking "Afghan fighter"...cradling a Martini-Henry rifle which seemed in darned good shape.

I wonder if he was a handloader????

[HTRN]

You think that's bad? I have an MH made in 1872, that's on it's third incarnation. It was rechambered in 1903 in .303, then at some later point(I'm guessing the 20's), it was put back to .577/.450 and issued ot the Irish militias.

It will fit a "minus" .450 pin, but very tightly. I've yet to do a cast to get the groove size, or the size of the throat.


HTRN

[The Double D]

Gents I am not asking about a specific rifle I am asking the theoretical based on the description given.

From the description given, what would you say the correct bullet diameter would be for the described bore.