But was your rifle modified from a standard 8x57mm action, either military or civilian?

I ask because, prior to WWI, Mauser did make M98 actions for Rigbys that had a slanted magazine and were specifically designed for the .303 British. Then, following on from that, a number of German gunsmiths started making M98s in .303 British, using the same action, but only for the German market - yes quite odd, don't you think?

Could your rifle have been on of these German made .303s with a slanted magazine?

I did see one of these rifles for sale, here in Australia, about ten years ago but, in the couple of hours that I went away to research it and find out what it was (I had never seen or even heard of one before) someone else bought it (drat, curses, damnation!). The price was only $450 and I should have bought it first and then researched it!!!!!

My .303/270 rifle has the standard M98 box magazine that was intended for the 8x57. I have been playing with it and it will take three (3) .303 rounds provided I am careful how I load them into the magazine, with one (1) 'up the spout' for a total of four (4) rounds. The rounds do not sit well in the magazine but they do remain roughly in place. It is not an ideal arrangement but it does seem to feed and eject reasonably well, although it could be a bit 'dodgy' when hunting in rough conditions. You wouldn't want to be facing down something that could 'fight back' with this rifle as it is.

It is likely that, when I have some .303/270 rounds to try, that they may be an even poorer fit, due to the smaller diameter of the projectiles, although the improved 'Magnum' case might compensate for that.

It is probably a bit of an overkill, but I am thinking of taking one of my spare M98 magazine/trigger guard assemblies and re-manufacturing it to duplicate the slanted magazine of the Rigby actions, at which point (if I do go this far) I will probably rebarrel the rifle to .303 British as the .303/270 bore is shootable but rough, and it would be closer to legitimate if it duplicated, or at least approximated, one of the Rigby rifles.