7x303 improved
MUCH bigger case than the 7x30
7x7.62x54R... in fact, there's nothing WRONG with the 7.62x54

jeffe

Here is another case to toss out, .348. Necked down to 7mm and improved would be interesting.

If your going to use a single shot action then several cartridges would work, but never use a rimmed case in a bolt action, thats begging for trouble and I am assuming your 280 is a bolt gun unless its a Ruger No.1 in which case I wouldn't mess with it just to have a rim....

The 7x57R or 7x57R IMP. would be my choice for a single shot rifle. The IMP version will duplicate a .280 Rem for all practical purposes.