Prolly talking about A bbl block and free float action like Mystic did on a stevens action.
Then sleeving the action will have no benefit as I have already proven.
See my website or 6mmBR.com gun of the week #75 (link in sigline below) for pics of what is being refered. Both of those use repeater actions and there was zero problems getting them to shoot superbly.
Both have put plastic on the walls.
My use of the block was not for strength as much as a heat sink. With so many rds fired during a relay, the last thing I wanted to do was cook a barrel. The block acted as a great big heat sink and that worked very very well.
The extra benefit of supporting the weight of the barrel and reducing the barrel whip were happy byproducts.
The process of sleeving is to increase the rigidity of the action so BIG HONKING barrels can be slung on the front without bending. Think 1.5" dia. 30" and longer barrels WITHOUT additional support from bedding under the barrel.
how often is this done?
This process has fallen out of favor as the installation of the sleeve can cause as many problems as it tries to solve. Larger diameter custom actions and different styles of bedding are far more popular.
If you need big, make it big. Relying on a thin layer of epoxy can be problematic.
Even for the heavier barrels used in F OPen, all standard actions are plenty strong to support WHEN proper bedding is used.
About the only thing seen are larger custom actions like the Barnard. But even itty bitty XR100's are winning their fair share of plastic.
YMMV.
Jerry