Conventional wisdom suggests that we should use a filler in our muzzle loading revolver loads for two reasons.

1. To eliminate an air gap in the chamber which might result in an inconsistent burn rate.

2. To place the projectile closer to the breech thus allowing it to engage the rifling without a jump if it were to be seated deeper within the chamber.

My question takes us back to the time before the breech loading handgun ban in 1995 when smokeless powder was the most common propellant. Back then, the standard .38 Special revolver target load was around 2.8 grains of Bullseye behind a 148 grain Wadcutter lead bullet. The tiny amount of powder would have left a huge air gap in the .38 Special cartridge case and the Wadcutter bullet itself would have been completely seated within the case resulting in quite a big jump before the bullet entered the rifling. So, why is the use of a filler considered essential when using black powder loads, but doesn't seem to be necessary when using smokeless powder ?

Regards
Brian