You get the idea. If I put 10 gr unique in a .38-55 case with a 250 gr bullet, do I need a filler? If the case density is lower than 50% is it unsafe?
I hope to be making my 1st loads for this cartridge this weekend, and the only other high density powder I have is Trail Boss. Can I go 10 gr or lower with unique safely, without a filler? I can pick up some Dacron if I need to.