Taylor Knock Out Value and the Thornily Relative Stopping Power methods are better gauges for heavy/slow projectiles than FPE. There is a Taylor KO calculator on this site and Thornily RSP is on Beartooth Bullets site.

http://www.beartoothbullets.com/rescources/index.htm

Experience is the best teacher, hunger good sauce.
Osborne Russell Journal of a Trapper