I would like to make some dummy rounds for my .404J before it arrives. I have brass and bullets but I don't know if there is an "accepted" over-all length for a loaded .404J round. Can someone please help?

The OAL of a cartridge (for the 1,000th time) totally depends on the bullet you are using and the dimensions of YOUR rifle's magazine and chamber.

Most .404jeffery's are cut w/ a short throat. I load 380grNF & 400gr Woodleigh to 3.58" in my M70.

Cpi is 3.52 OAL. Most modern actions can accomodate 3.6 OAL.