xausa may be spot on.

From some reports on another forum the rechambering of 9,3x57 rifles to x62 was common. My x57 rifles are marked "9,3mm" only. But they are x57. Yours might indeed be x62. A chamber cast may be in order here.

Having said that, I do believe xausa may also be correct in his other guess: a 9x57 chambering. Hard to see how you could have chambered a 9,3x57 round, but if perchance you did the result might be as described.

I've never seen a spoon bolt on a 9,3x57. Such an appendage is not common on such rifles. Could easily be that the rifle had one, or I wonder if the bolt was a replacement without regard to headspace.

Lots of guesses but no real answers I am afraid to say. Maybe give the chamber cast a whirl and see what it turns up.