Circle Fly - call Craig and ask a lot of questions. He is a wealth of info.
http://www.circlefly.com/html/welcome.html

For a lot of dodads... Track of the Wolf
http://www.trackofthewolf.com/

Also Dixie Gun works
http://www.dixiegun.com/

Lyman published a book about black powder. While really meant for muzzle loaders, it had some good info regarding pressures and loads.

Pete