Not to add fuel to the fire but I'm having trouble getting my head around, how a wad, as described by Mr Louis, managed to stop sideways, halfway down the barrel, when upon ignition, it would have been slammed against the bullets base and then propelled down the barrel at probably 1,600 fps,hard up against the base of the bullet, just wondering.
It is my understanding that Mr H Pope, considered that the advantage of muzzle loading the bullet was in the fact that any metal displaced, as the bullet was forced into the barrel, would be towards the front of the bullet, thereby having little effect on accuracy.
A simple test of bullet metal displacement can be done by simply breech seating a bullet and then pushing it back out and examining the base, where you will find some evidence of fining.
Perhaps making the bullet diameter slightly smaller than the groove diameter may reduce this fining, as may the effect of a wad made from a material such as LDPE hitting the base of the bullet with considerable force during ignition. Guess we will never know.
Mike.
Just my 2c worth