Mike,
it is still a .450/.577. The lead I shoot thru it is about .461. I have had a little luck before I began this project with patched .458 barnes bullets. The good thing about this is, if all copper slugs are hard on these old barrels, by patching them, it should prevent any potential damage.
I cheated a little and use teflon pipe tape for the patch material.
Jerry
Having bought my first Martini-Henry 577/450 Service rifle over 45 years ago so I have some experience in reloading them and making pp bullets.
The steel used in these barrels is soft and wasn't intended for anything but lead bullets. Jacketed bullets will wear it out very rapidly indeed. The bore is tapered from the chamber to the muzzle so as jacketed bullet will not 'bump up' to fill the bore perfectly as a lead bullet does. The bullet should be bore dia, patched up to groove dia. The paper patch patch should be cut by the rifling as the bullet travels through the barrel and seperate from the bullet in the first few feet of free flight. Failure of the patch to detach or only partially detaches will result in very poor accuracy indeed.
Applying the patch is fiddly at the start but you soon get into the swing of doing it. The turnover of the patch at the base of the bullet should not exceed 1/8" to 3/16", Don't make it over long and never twist the ends into a pigtail. If the parch is slightly damp (use a plant misting gun)a very light spray will help the patch to adhere to the lead and it will shrink and tighten when drying out. Standing the patched bullet upright after patching will hold the paper turnover in place while the patch dries. Ideally use a smooth bullet without grease grooves. PP bullets always had a grease cookie below the bullet.
Have fun reloading.
Harry
