The Americans and others use saboted bullets - not ball - in a particular type of BP firearm, the in-line rifle/carbine. The use of a sabot enables you to shoot a nitro-type bullet at fairly high velocities from a BP rifle that looks more or less exactly the same as a bolt-action nitro rifle. They are called in-line because they use a #209 shotgun primer on the head of a regular-looking bolt. Loose-loading CAN be done, but most in-line shooters use this kind of gun because they usually shoot them by inserting one- two or three 50gr Pyrodex pellets into the breech, rather than loose-load down the muzzle, like the usual muzzle-loader does. It is therefore very difficult to adjust loads, since so your load would be in multiples of 50gr - not ideal unless you are aiming to emulate nitro-loads in a BP rifle...hence the use of sabots. There is a very noticeable difference in shooting 2x50gr pellets and 3x50gr pellets or even, as some do, 4x50gr pellets. x 10
I've only ever seen one here in UK in .54cal, and the owner got rid of it as soon as he could, due to the lack of the Pyrodex pellets that the thing used. Quite what bullets he shot in it I don't know, but they must have been quite large.
The in-line is a way of shooting a BP rifle in the BP hunting season in the US and Canada that looks and feels just like your nitro centre-fire rifle. Some states even have a separate 'in-line' season of around seven to ten days.
Not my thing, I'm afraid...
What kind of gun are you keen to try this kind of load in?
tac
www.muzzleloadingforum.com