Al- I presume your gun is a smoothbore? A friend sent me some of the Lyman slugs to test in my .12 bore pump. One of these days, I'll put the mag. pad on my shoulder and try them out.

A double 10 bore would be fun for sure. I think I'd prefer the tubes to be 24" or 26" though.

A pure lead ball at .774" will be a heavy one, that's for sure. 10 to the pound = 700gr. Keep in mine, a 10 bore shot cup with slightly reduced petals may contain a Lyman .735" ball perfectly, or 12 bore wads placed inside the plastic wad can give the correct height for crimping. Some of the guys got fairly good accuracy from their cap-lock 12's shooting 20 bore balls in trap wads (BP shotguns) The same configuration should give reasonable results from a 10 - ie: the Lyman .735" ball - standard mould.

Once a guy gets a good load for round balls in these smoothbore guns and actually tries them on either game or in penetration tests, he rarely even thinks of factory slugs for his gun.

Some time ago, I attempted to get a friend to cut the tubes on his double .410. After measuring up the wall thickness, I concluded there was enough meat to rifle them. The 3" .410 shell holds more than enough black powder to launch a sized 350gr. slug at about 1,340+fps, matching some of the 1870's buffalo .40's. I'm not sure how much the pastic case would hold, however one might use .444 Marlin cases fireformed - just an idea - no practical testing on that as of yet.

I hadn't thought of using factory slugs or round balls in a .410 due to the small size and light weight, however do recall a .410 'vermin load' mentioned in an article using 3 or 4 undersize balls (000 I think) with just enough Unique or Herco to get 1,300fps. These were loaded in .444 Marlin cases and shot from a Marlin rifle. The same idea could be made to work in a pelter(shotgun).

For rifling, if that's a idea with merit, it would be a simple matter to use a .45 cal. rifle barrel with an 18" twist as a guide for the single tooth cutter for the .410 bores - as was done for rifling muzzleloading barrels in some back-woods shops.

The same idea could be used to scratch some grooves in a cut-back smoothbore of larger persuasion. www.trackofthewolf.com sells muzzleloading barrels for less than $100 in .54 cal having 80" of twist. The 12 bore Lyman slug would benefit some as would any round ball load. The rifling wouldn't have to be deeper than about .005" or .006" to be effective in assisting with accuracy. In a 12 bore, if tightly patched inside a plastic hull the .715" ball could give game killing accuracy to as far away as you could hit a deer, moose or bear in the vitals. That's .545gr. for the .715".