Be cautious with R.B. actions that have been converted to shotguns.
Warn block pins and worn holes through the blocks may well mean a major restoration to make it a shooter.
It is not so critical in a shotgun but in a brass case a block that has some give or does not stay perpendicular to the bore when you fire it can cause uneven stretching of the brass.
Uneven case stretch is easy to check on a R.B. as you can fire a cartridge, then chamber the fired cartridge 180 degrees from the position it was fired in and close the block. If the hammer binds on the block in the last few millimeters there may be a problem.