One of my first projects back in school was a shortened 1891 Argentine Mauser converted to 222-size bolt face. It was a single shot by necessity rather than choice since back then I hadn't yet figured out how to make it a repeater. Long since traded off.
The 91 is one of the simplest to convert to a different case head since it's a push-feed; it's comparatively easy to re-heat-treat the smaller extractor after welding to lengthen the hook. I've used both soft-solder and epoxy to affix the collars to the bolt faces, with equally-good results. On the single-shot I used a wooden block for a loading ramp but coulda/shoulda used a steel plate to fill-in and thus 'rigidify' the receiver. It's also easy to convert to upcock with short 3/8" striker fall if wanted.
Later did a sporter conversion of a Mauser military trainer in 22LR, a splendid little single-shot squirrel rifle with Leupold variable, ebony forend tip & grip cap, figured walnut, low bolt handle & safety, classic-style straight comb with cheekpiece, etc etc. I and the owner always planned to do a magazine conversion for it but never got a tuit. Wish I had a photo of it but I never owned a good camera 'til the middle/late '90s.
Regards, Joe
