I'm gearing up to load .44-40 for my Miroku Winchester 1873 and was researching bullet diameter for the .429" bore in a gun chambered for cartridges that use a .427" bullet. Cartridges with .429" bullets will chamber I'm sure, but trying to achieve the usual .001" - .002" over groove diameter for cast bullets, I very much doubt. I discovered that many original Winchesters had oversized bore diameters but they still shot well. Reportedly because bullets were very soft and the base easily obturated to fill the grooves. The blue label in this box stresses that pure lead must be used to cast bullets. Other articles confirmed that this works with smokeless loadings as well. Magtech in fact produces .44-40 Cowboy ammo with a bullet alloy BHN of 6, or almost pure lead. Though .427" bullet diameter, these are accurate cartridges. An American Rifleman on-line article using smokeless powder loads with soft .427"cast bullets shot through the .429" bore of a replica Henry produced the same decent accuracy similar to .429" bullets. (Handloading the .44-40 Win. - American Rifleman) The bullet lube recipe advice is also interesting in its' simplicity compared to lubes today. Just mutton tallow or Japan wax, which apparently worked fine. I would enjoy hearing from the experienced Old West members who load this cartridge a lot.