> Chamber pressures in cartrige arms are influenced by the charge
> weight as well as the projectile weight. Not sure that applies to
> black powder or not since most charges are determined by volume.

Chamber pressures with black powder are also influenced by the
ammount of powder and weight of the projectile. It is less sensitive
to variations in the powder charge, which is why it can be measured
by volume rather than by weight. However, if you get carried away
with how much you pour down the barrel and/or have a large, heavy
projectile on top of it the laws of physics still apply and pressure
will increase significantly.

Short starting the bullet, i.e. not seating it on the powder, will
cause the barrel to bulge at the location of the bullet in the bore.
Couple that with a doubled powder charge and the chances are very
good that the gun will blow up!

> Also I'm having a hard time locating load and pressure data. I've
> heard the Lyman's black powder manual is good. Any one ever read it?

Lyman's is a very worthwhile book to have on hand. If you can find
it, get the original edition but the present one is also good. Some
of the tables in the old one have been replaced with other material
in the new one, otherwise they are both excellent references. I
reread mine over the Winter, and often refer to it.

-Kees-