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In looking forward to reloading for both my rifles I have noted bullet sizes mentioned as .460+ for the Martini and .585+ for the Snider. My Martini will not begin to swallow a .457 round ball (I didn't attempt to pound it through) and my Snider sporter will engrave rifling on a .575 minie ball. I hope this is within expectations.
The Martini Bore is an extremely complex geometric vessel. It is made up of flats and peak and some long tapers.
https://www.milsurps.com/images/impo...tandard-43.jpg
Start with septogon- a seven sided polygon. Like an octagon barrel, the center of the flats has a smaller diameter than the corner. In a septagon a confusing issue is the flats are not across from each other, so measurements of the diameter is not easy to make.
In the corner of each flat of the Henry barrel is a peak.
https://www.milsurps.com/images/impo...tandard-44.jpg
The diameter of the top of the peaks is the same as the diameter as the center of the flats. I refer to this as the minor diameter. It's not the land diameter as Henry Rifling doesn't have lands.
In the Martini Henry this minor diameter is .450. This is why your .457 round ball won't go in.
The second measurement is the corner of the flats. Remember on octagon barrel the corners are greater diameter than the flat, same thing in the septagon Henry barrel. The corners of the flats of the Henry barrel are also greater.
As noted above each flat has a peak in the corner. The depth of the corner of the flats at the base of the peaks is .007.
I call the diameter of the corners of the flats the major diameter. The major diameter of the henry bore is .464.
It would be pretty simple if this is all there is to the Henry bore. The Martini has another factor, a long tapered throat.
The first 24 inches of the bore from the muzzle is as described.
The last 8 inches to the breech is tapered. The taper starts at just in front of the chamber. The major diameter is .469 and the minor diameter is .451.
.458 diameter bullets shoot in the Martini bore. .464 bullets shoot better, .468 bullets shoot best...unles you have a pattern A or B MKIV.
Can't help you with the Snider, it's a modified muzzle loader.
WOW, I had no idea this was so complicated. Thanks for stopping me from going the wrong direction.
Just took the easy way out and bought 20 rounds of both, 10 X ammo. from IMA.
Ten-X ammo has undersized bullets. Brass is great.
"...577/450 and 577 Snider..." Different cartridges. The .577-450 uses a .460" lead bullet. The .577 Snider a .577" lead bullet.
I have a how-to to make reloadable .577-450 cases out of 3/4" brass bar stock with BP load data, if you want it. toheir@hotmail.com
Oh and http://www.youtube.com/watch?v=1csr0dxalpI
The Martini uses a .468 bullet and the Snider bullets are closer to .585 and .590 depending on which you have.