I believe that existing regular (hardened) actions were modified, not purpose-built for the .22. Somewhere I have seen correspondence regarding annealing  them to allow the caliber stamping. What else was done to them, I do not know, but surely removing a portion of the rail would have required softening in that area as well. As to whether they were re-hardened, that would probably not have been considered necessary, since the action was monstrously strong for a .22RF, no matter what. My GPR bolt is 'sticky', but I attribute that to a less-than-perfect plate system, which binds slightly.