Undersized boolits and leading

[JeffinNZ]

Team.

So if an undersized bullet will likely result in leading why don't the big .58cal Minie rifles lead up? It the leading linked to smokeless powders?

[Bret4207]

Black powder, as I understand it, has much more of an explosive burn rate and causes the boolit to obturate or swell to fit the barrel. This is especially noted in hollow base designs. Smokeless is more of a burn than an explosion and the pressure curve is far different.

IMO, and it's only an opinion, leading is primarily caused by poor fit, either static (undersized boolits for instance) or dynamic ( pushing it so hard it strips). Other causes can be poor lube, rough barrels, constrictions, poor designs, over obturation. But in my mind FIT IS KING, it's the first basic step in successful shooting. Most of my failures, and I still have a lot of them, are directly related to poor fit.

[44man]

Yes, mostly but you are also lubing the bore when you load too.
A BPCR can lead up but it is far less then smokeless will do.
BP has lower pressures and even though it burns fast, it still burns progressive down the bore and kind of cushions the push.
One thing we found with a Minie' ball is they have very poor accuracy and we had trouble keeping them on paper at 50 yards. By lapping the molds and getting a snug fit, we were able to clang the 200 meter gong. Improvement was amazing.
Bret is right, even fit works in muzzle loaders.

[fatelvis]

The .58 caliber Minie is undersized when loading it down the bore. It has a hollow base, that upon powder ignition, conforms to the walls of the bore/rifling. This was a huge improvement from patch and ball, because after the Blackpowder fouling build up after a couple shots, the p&b becomes increasingly more difficult to load, where as the Minie, being undersized at the time of loading, remains easy to load.

[303Guy]

Another point that is overlooked is that black powder forms a wad behind the boolit as it burns. Also, the hollow based minni ball gets rammed down hard onto the powder which likely expands it right then and there. Or at least it would have on the battlefield.

This effect can be seen on the high speed clips on u-tube. When a revolver is fired there is flame escape at the cylinder gap but only as the flam front passess over thereafter the only smoke escapes until the boolit exits the bore followed by a big flame.