On a range day larf, while shooting my semi-dedicated .22 upper (it has a CMMG conversion bolt installed full-time but I can drop my 15 carrier in if need be) a friend and I had a discussion about uppers, caliber versatility, ammunition commonality and the possibility of building up a Marlin 1894 as a kind of scout rifle, throwing a low-powered optic on the thing and firing the same ammunition I shoot through my preferred sidearm (SW 586 .357m).
Then the gears began to mesh and we had a eureeka moment. Why not just drop on a .357 upper onto my existing lower?
So. Has somebody done such a thing? I did a little googling about and discovered a thread over on THR where they briefly mentioned ".357 Magnum Rimless" as an AR upper variant, but didn't really go into any detail on it. I don't really know what a Magnum Rimless is, but I'm just going to take an educated college-boy guess and assume that it's not the same cartridge as I fire through my revolver.
I was thinking that it wouldn't be entirely too difficult to build up a .357m/.38spl upper. It'd simply require a modified bolt face (wider for the rimmed case, with a deeper extractor), a 9mm barrel chambered for the magnum cartridge and a half-staggered magazine like those Black Dog makes for the .22. Naturally if they were in the 30-rounder form factor, they'd be limited to a capacity of 10-13 rounds.
So, has anybody already done all the hard work on this? I didn't find too much via google and figured I'd pick y'all's brains.