As already stated , Rugers are pretty stout.....that being said....when I check a used revolver, first , I check for cylinder gap....most Rugers seem to fall in the .003-6 range. The smaller the better to a point. If its too small, it may bind when it gets really fouled. Too large ....ya loose a lot of gas , and fps. I really don't know what Rugers specs are....I know I've check my "new rugers" , and some are as large as .006.......My 4" redhawk was .0035 OTB.
My SRH 454 was .006.......seems to shoot fine. Secondly , I'll cock the hammer.....keeping my thumb on the hammer , pull the trigger and hold it back while easing the hammer down...keep the trigger back. This will lock everything up...or it should. Now while holding the trigger back , check the cylinder for various movements....in an ideal world , there shouldn't be any. Take a bore light....check for flame cutting under the strap....check the forcing cone ...check for leading , though mostly that can be cleaned out. Also if the dealer will let ya....drop a live round in the cylinder, make sure it will chamber....as in 357s or 44s,this will be sure there is no issues like ridges or cutting from someone using "specials" and not proper cleaning. (more than likely a gunshop will not permit a live round and the revolver to be together ! ) Thats the way I do it....pretty much like others have said....only tools I take is a bore lite and feeler guages.
Good luck.....regards IROLD