Originally Posted by Jim K
... Even so, all the precautions apply to taking the grips off and taking the assembly apart. The original grips are gutta percha (hard rubber) which becomes brittle over time, so trying to take that assembly apart can result in cracking the grip. ...
A special thanks goes to Jim K for reminding us about the risks of tinkering with original hard rubber grips. The stuff does not age as well as wood, and at this late date many originals are warping, shrinking, cracking, even crumbling. They can crack without any "help" from a human hand. The modern-made plastic replacements by Vintage reproduce color and texture of hard rubber as newly made, but probably won't age so nicely. It's not really known yet, since another hundred years or so must pass before we can be surer.
It might also behoove us to remember that all plastics above 50 years in age can deteriorate in ways that might ruin the guns they're installed on. This applies across the range of countries and manufacturers: I've seen it happen to WWII Walther pistols, 1950s Beretta handguns, "Tenite" installed as a non-hygroscopic wood replacement on budget shotguns, and various other pieces. Even "Coltwood," a vaguely wood-esque plastic Colt used from the 1940s onward, is warping.
The best (in terms of retaining original dimensions and strength/wear characteristics) seems to be the DuPont nylon formula Remington used in its Nylon 66 and several other 22 rimfires. Be warned that many specimens of the Nylon 66, 76, 77, Mohawk 10c, and Nylon 10/11/12 are now suffering cracks. Replacements are simply not available. It is unclear at the present time (2011) whether the material is aging, or if poor use/storage conditions pertain, or design shortcomings are making themselves felt (in fairness to DuPont's materials engineers and Remington's design teams, they could not predict 50 years of use by the public - espcially not the myriad ways in which some members of that public contrive to abuse and neglect arms). Most cracks occur between the sear pin and the top of the stock, near the rear of the sheet steel receiver cover, where the striker spring and its guide press against their rear anchor point. The Nylon 76 (lever action) seems to be the worst offender, as it is a true locked breech arm, but the locking bar braces against the rear of the stricker slot; metal - on - metal locking does not occur, as it does in the 10/11/12 (all bolt actions very similar to the 510/511/512).
Many of these rifles have been left in a cocked state for decades on end, and there are no metallic reinforcement rods, sheets, nor bushings - only structural nylon to absorb the loading, tension, and leverage. Snap your Nylon 66 and relax the spring without delay.