What would be the correct loaded overall length for this magnum?

Thank you.

I can't answer the question, but there was a guy(who's forum name is 30Hart) on the Cabela's forums who shoots that cartridge and claims to be good friends with Bob Hart. He is really helpful, although I haven't seen him post in a while. I guess for that matter you could look up the Hart website and give them a call. Hope this helps.

Sorry, it's just NOT that cut and dried easy.

The "correct" OAL for any cartridge is one that will feed properly, chamber well and shoot accurately. That doesn't come from a book, an expert, the stars, etc. It takes thoughtful cartridge assembly and target analysis from loader experimentation with HIS load, in HIS rifle.

More than likely Hart chamber that rifle and they are still selling 30Hart brass/dies. I agree with dlulter give them a call

Robert W. Hart and Son Inc.
401 Montgomery St.
Nescopeck, Pa 18635

Phone Toll Free: 1-800-368-3656

Gentlemen, thanks for the responses. I did give R. W. Hart a call and the answer I recieved was to magazine length. Big help, thank you very much. Finally got the bro in law to have a loaded round measured with a calipher and it came back the same as the listed maximum overall for the .300 Roy... the parent case. The load specifications were inside the box of cartridges from HART, but a length was the missing information.