Sorry guys - I missed this trhead for a few days(weeks?).

I'm using 14 bore wads in a 16 bore DB Hammered Husky of 1898 vintage with shot loads using MagTec brass. The gun is actually chambered for paper hulls for the shot barrel and brass for the rifled 13 bore tube, which fits circle-fly wads OK.(the chambers are identical, btw. The 14 bore wads are necessary in the 16 bore shot barrel to take up the space in the brass hulls - or, I can use plastics as the chamber is actually 68mm long, without any undue pressure.

I would not worry about using 10 bore wads in the 12 bore magtec cases, but would be on the lookout for paper hulls to allow the use of normal wads. As with any loading, start conservatively watching for any pressure signs.

The primers used in shotgun are usually good for showing this. Pistol primers (used in Mag Tec brass) will not show such pressure signs as they are designed for pressure which could actually blow the gun up, most likely, and therefore are of little or no use in showing pressure in a shotgun.

I would not use balls that are oversized in the smooth portion of the bore.

The cup wads that Tinker (hollowed fiber) and I use (cup of plastic) keep an undersized ball from touching, yet centred in the bore while the wad itself seals hard against the bore's walls, should take the twist of the tubes and impart that spin to the ball for stabilization.

Well, in theory it should work - and does seem to work in my rifled 12 bore pump - using the undersized ball. I've only shot it at 25 to 30 yards and received an inch and a 1/2 hole for 4 shots. At the same range though, my double smoothbore did produce about the same sized groups. I'll need to try this rifled 'camp-gun' out a bit farther to be sure.

Just re-barreled my gopehr .17, so my thoughts are elsewhere for a while. The double rifle/shotgun with it's patched balls and the 12 bore pump will have to wait a bit.

Good luck.