Mr. Housemen, thanks for your question because it makes me realize, once again, how far the progress of accuracy development has marched beyond what was once considered "state of the art." So go back to the '50's and '60" when Benchrest shooting was getting popular and attracting accuracy rifle buffs and like-minded gunsmiths. Remington's M-722, followed by M-700 and XP-100's had changed the game and become the core of most bench rifles. But successful as they were, advanced thinking experimenters and gunmakers like Ed Shilen made them even better by making close fitting "sleeves" that make them even stiffer and provided a flat-bottomed "footprint" that made bedding more secure. The sleeves were held in place by expoxy or other types of cold solder and made the sleeved action a single rigid unit. Sometimes the donor receiver was even lightly turned to ensure a perfect fit and pressed into the sleeve. Occasionally you still see sleeved actions on the shooting circuit but they have mostly been replaced by more modern target type actions that duplicate what was trying to be achieved with sleeves.
Excuse my long-winded explanation, so here are a couple pics to better show what I was trying to explain.
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