Was kinda throwing the idea around last night, doing a small amount of research (maybe not enough)...
I was thinking...
If I were to take a .22wmr bolt action rifle, like a Marlin 982 with stainless bull barrel, and granted I could find the right drill bit and a drill press, I think I could build a 5.7x28mm precision rifle!!!
According to Wikipedia (only place I found a good comparison table), the differences I've found were:
Shot: Rimfire vs. Centerfire, though possibly switched by simple grinding/filing (with hardening of course)
Chamber: Straight cartridge at .241 as opposed to .310...
Also, the 5.7x28mm has a very steep shoulder angle, which would probably be about right with just a standard .310" drill bit...
Whaddya guys think?
Would a .22wmr bolt catch and hold a 5.7x28, or would I have to increase the diameter by .019? How would I go about doing this?
Does the Marlin 982 have a center-to-rim pin block, or an off-center-to-rim pin block? This is crucial if I'm going to try and cobble the firing pin from a rimfire firing pin block...
I'd probably have to chase the new chamber with another smaller bit to make a pocket for the neck, which could be the 2mm difference between lengths. I haven't looked at a .22wmr up close yet...
Think the .22wmr bull barrel would hold up to the 5.7x28mm chamber pressure?
I think it'd be way neat to have a 5.7x28mm precision rifle, especially if I could cobble a mag adapter that would hold Five-seveN magazines... That'd be later... MUCH later. For now, I'd go with just standard single-shot until I whip up a magazine solution.
What about mags? Would the 7-round 22wmr hold 5.7x28mm? What about the ejector size? Would I have to move it back 2mm to accomodate a longer round, or would it still be able to kick out the 5.7x28mm?
Does anyone have a Marlin 982 in .22wmr and access to a 5.7x28mm round? Or just a .22wmr and 5.7x28mm for visual comparison?
 Is there anything else I need to know about swapping calibers? Am I underestimating the job? [/edit]