One problem you may have is that different "standard calibers" often vary slightly from maker to maker. For a while the "production" rifles like TC seemed to use a samller ball, like a 440 or 490 for their recommended loads. A custom gun with a Douglas barrel definitely wanted a 445 or 495 ball. As to a universal, especially for a hunting load, probably a 490 in a 50 for instance, or a 530 in a 54 would accomodate almost all barrels with a harder cast ball. I believe Hornady makes a 485 hard cast for that purpose
. Lloyd in the 50 cal and moose thread stated the results of his test with just a slight hardening of lead, about 50-50 lead WW. Its about the same as the birdshot alloy I use in cast bullets. A little bit of hardening can go a long ways. They used to use just tin. Personally I think the .010 under is about as close as you can go. Some older foerign made ML's may be too tight but for most modern made guns it should work.
DP