I agree (strictly my amateur opinion, no official expertise) with Chuck on this and would like to add that the pressure 15" from the breech is going to be relatively low. The Dupont pressure curve chart that I and many of us have saved, shows less than 4000 psi @ 10". 15" will be somewhat less than that.
Superposeds, while pretty reasomable, are hardly a "dime a dozen". Get a real expert's opinion and go from there.

> Jim Legg <