Help needed: bad bore pitting at muzzle in BP cartridge rifle

[GrantR]

Here is a quick digital photo of my latest firearm acquisition - an 1872-dated BSA Ltd. Mark III Snider-Enfield two-band rifle, with Canadian markings: DC-in-diamond, issue mark to 39th Norfolk Battalion of Rifles, formed in 1866 with headquarters at Simcoe, County of Norfolk, Upper Canada (Ontario).

As you can tell, she's "been there, done that" during her 114-odd year lifetime, and has lost her clearing rod in the process, but everything is tight and fully functional, action-wise. The five-groove bore looks great (mirror bright and shiny, with sharp rifling and virtually no pitting) for about 95% of its length. Unfortunately, the last inch and a half or so, at the muzzle, is badly pitted. I have cleaned that up as well as I can, and must now fire a few rounds to get some idea how it will affect accuracy. However, I fear that some relatively drastic remedial measures may possibly be required.

If so, I certainly don't want to shorten the barrel to get rid of the offending area. I seem to recall reading about having such a problem area counterbored to remove the pitting (and rifling for that short distance) with a new crown effectively being formed at the end of the counterbore, so that the bullet exits the rifling at that point, but the outward appearance of the rifle is unaffected. Does anyone have any experience with that sort of "fix" - or have any other suggestions, for that matter?

 

[tiriaq]

I would be a bit concerned about the effect of a counterbored muzzle on a hollowbased bullet. Do you think that the skirt would try to expand to fit the counterbore diameter? Probably by the time the bullet has reached the muzzle pressure may be low enough that this wouldn't happen. I do not know if this might happen - just a thought.

 

[GrantR]

Actually, I won't be using a hollow-base bullet - recommended practice nowadays (developed over the past couple of decades or so by folks trying to get Sniders to shoot) is that a solid-base oversize bullet works best for accuracy (as it does with breechloaders generally, of course) rather than a hollow-base undersize bullet. I will be loading with an over-bore-size (.590") solid base bullet, for which I already have the mould (for the 3-band Snider I already had.)

The original Snider cartridge was designed around a hollow-base minie-type bullet - as were the umpteen subsequent "Marks" of Snider cartridge they tried while attempting to achieve decent performance. In fact, the problem primarily lay with them using the same under-bore-size bullet as had been used in the muzzle-loaders, and then variations of that bullet. They never did manage to duplicate the accuracy of the muzzle-loaded versions: the Snider conversions were simply less accurate than the rifle muskets they were made from!

As I understand it, the "explanation" goes something like this: peak pressure with black powder occurs right at the moment of ignition and falls off thereafter - thus maximum skirt expansion of a minie-type bullet occurs right at the moment of ignition, so that type of bullet performs well in a muzzle-loader - especially with the progressive depth rifling of the Pattern 1853 Enfield (grooves deepest at the breech, and getting shallower towards the muzzle). However, in the breech-loaded Snider version, that same bullet is crimped into a cartridge case, preventing skirt expansion until the bullet has cleared the case mouth. Once it has moved even that short distance, much less skirt expansion can - or will - occur, and you have more windage (and noticeably poorer accuracy) than with the same bullet fired in a muzzle-loader. Admittedly, the different versions of Snider cartridge almost exclusively used coiled brass cartridge cases, so the constrictionat the case mouth was perhaps not quite as bad as it would be with a solid brass case - but of course all we can load with nowadays are solid cases ...

 

[pengfire]

Yes, the counterboring can eliminate the pitted area without looking bad from the outside. I did this on a Model 94, a fair bit larger than the bullet diameter (0.5" vs 0.452") and accuracy was unaffected. This was for cowboy action purposes though so I can't comment from experience on long distance shooting. Good luck!