Looking for some help to I.D. cartridge case

I have had this cartridge case for a long time and believe it might be a proprietary cartridge for Guns & Ammo magazine. the headstamp is NORMA G&A SPECIAL.

length 2.86 inches rim diameter .540 inch outside dia at case mouth .525 inch and inside diameter at case mouth .500

Either it was developed for a special Guns&Ammo rifle or just a case manufactured to be used in forming other calibers. Note it is without a belt but could be formed for some
of the old Newton cartridges. If G&A used a rifle I would think that it would be a Mauser type. Photo shows the G&A case next to the 7,62x51mm NATO cartridge.

I am unable to find out anything and any help would be appreciated, RCSAttachment 89637Attachment 89638Attachment 89639

Found these after a little scrounging 460 G&A Special I think it may fit the bill as you would lose a bit of length when neck sizing and the dimensions are pretty close not exact but fairly close built on a ZKK602 apparently.

CINDERS, Thank you, I am certain that is the case necked down to the 460 G&A Special built on the magnum Mauser type actions. I looked all over but was unable
to find anything. RCS

No probs RCS I enjoy looking for cartridges as well as collecting them have not been doing to much lately will have to start looking again my last big buy was some months ago a 75mm QF French case from WWI in very nice aged condition. So now its just wait until a 75mm French WWI French projie jumps up!..........