The best thing about the WSSM's is that they fit the AR15 magazines. Prior to that, the only way to get an AR in .243 or 25 caliber was to step up to the AR10 platform which is several pounds heavier. Last time I looked, DPMS offers WSSM's off the shelf and several custom AR makers have specialized in them.
If anyone is still making them in bolt guns, don't think they will be for long as the 243 WSSM only beats 243 Win by about 100 fps and the 25 WSSM no better than a 25-06, so stocking up on brass/ammo probably not a bad idea.
Regards,
hps