Here's an article I stumbled upon.  Makes for an interesting read.
 
http://www.castbullet.com/shooting/rb30.htm

That is an interesting article.
 
Good luck with LA. F&G
 
Paul

I recall a similar article where a fella rigged up a 7.7 Arisaka to shoot cast lead balls over a light charge of Unique.  Claimed it was pretty effective on rats in his wood pile and because of the long barrel, was also pretty quiet.  
 
The castbullet article is the best descriptive one I've seen yet.  Very good illustration of  how small changes in charge weight can translate to significant changes in pressure.
 
I "experimented" in using Red Dot to push a lead lap to fire lapp a barrel.  A very small charge would send the lead billet down the barrel, but stick just short of the muzzle.   A very small increase in charge in the next round (after I tapped the prior billet out) would send the billet (now bullet) flying into my backstop, sometimes with suprising penetration.
 
If I fire lapp another barrel, Unique or 2400 would be the better choice.
 
Nels