Questions pertaining to charge:projectile weight ratios

[Naphtali]

I believe the generally accepted "full-power" black powder load for muzzleloading patched round ball is 3/7 (about 43 percent) weight of RB. In The Muzzle-Loading Cap Lock Rifle, Gorning's Formula shows this approximate powder charge:RB weight ratio to yield 1600 fps muzzle velocity, give or take.

In my copy of Muzzleloading with the Champions, published by the NMLRA in the early 1970s Walter Grote, in his slug gun interview, identifies 1:4 charge:slug weight as yielding substantially similar muzzle velocity. Slugs, the subject of the interview, have sectional densities orders of magnitude greater than RBs. Yet lower charge:weight ratio yields comparable muzzle velocities.

What gives?

I know gas blow-by occurs during a patched RB's travel through the barrel. But are other factors contributing to what appears to be a severe combustion inefficiency for RB propulsion compared with propulsion of slugs?

Parenthetically, is the same sort of propulsion advantage occurring with BPCRs - that is, charge:bullet weight is much lower than RB's, yet comparable muzzle velocities are obtained?
***
My questions are specifically not intended to include R.E.A.L. bullets or Minié balls, or non-mallet loaded conicals.

[newton]

I think weight has a lot to do with it. The heavier an object, the more combustion it needs to propel it. However, once started it seals and retains the energy behind it, utilizing it better than a light object. Heavier projectiles always produce higher pressures, which in turn produce higher velocities.

I believe this is what you are speaking of, but I have been known to completely miss a persons point.

[Omnivore]

My thought was the same as Newton's. The higher pressure behind the heavier projectile increases temperature, which in turn increases the burn rate. That's why the magnum smokeless rifle cartridges use the slower burning powders. You load them full of the fast burning pistol powder and your gun explodes.

So it's a balance. Same thing happens in your car engine. The higher compression chamber needs a slower burning fuel or else you get detonation i.e. the fuel burns too fast and pressure spikes. The same gun, with the same powder, and a heavier projectile represents a higher compression 'engine' compared to using a lighter projectile.

I've gotten more velocity from a 180 grain conical than with a round ball in a 44 percussion pistol, using the exact same black powder and charge weight, measured repeatedly, back and forth. Since it obviously takes more energy to accelerate the heavier bullet, the explanation has to be a hotter, more efficient burn due to higher sustained pressure during launch. Study loading manual data closely and you'll see this process in action. Gas leakage past the projectile has very little to do with it, unless you have a very poorly fit projectile.

Such exothermic reactions can get out of control, and besides blowing up guns, they have completely destroyed more than one chemical plant. Fortunately, black powder is relatively forgiving. More guns get blown up using smokeless.