Does anyone know what size shell holder the 500-450 Nitro Express uses. Looking at the dimension the rim diameter is about .006 smaller than the .470 nitro. Northern Shooting Supply lists the #55H as being the correct size. I have tried to email them but keep getting a mail delivery failure message. I ordered a set of RCBS Dies for the 500-450 nitro which was labeled as manufactured in 1982. The box listed the shell holder as being the same for the 450-400, which I know is wrong. I hope when they arrive they are in fact 500-450 dies as labeled.
Thanks,
Trooper 1919

I called Australia I got the answer to my question. A Hornady #55 is what the 500-450 nitro uses.

Just as an FYI.

Hornady lists the No. 55 shell holder as suitable for reloading the .470 and .500 NE rounds, both of which have the same case rim diameter of 0.655 inch.

The RCBS No. 46 shell holder is listed by that company as suitable for reloading the same rounds.

I don't know the answer, but it seems you should be on the right track as long as the .500/.450 has a case rim diameter of (or close to) 0.655 inch.

Thanks Michael, The dies and shell holder should be here in a couple days so I'll find out then

I use the same RCBS shell holder as the 500NE, assuming you are reloading the 500/450 3 1/4” NE. Have a couple shell holders for the press and bench primer.

Thanks Rockdoc, The dies came today and there was a shell holder with the dies that fit my 500-450 Nitro Brass. As hard as it might be to believe the dies are RCBS and have their original tag from 1982 and look like they were never used. I'll just have to see if someone has a load for this caliber. I have several books on reloading information for the old Nitro Express calibers but none for the 500-450 3 1/4 Nitro.