I consider any cylinder gap over .010 as excessive and .007 as ideal. Tighter is OK to a point (maybe .003-4"). That's my opinion. You may be able to narrow that gap a bit by tapping in the wedge a bit further. On several of my guns I have ground away part of the wedge spring on the top of the wedge to allow it to be tapped deeper into the slot to pull the barrel more rearward. That is usually doable on ASM & Uberti guns.
Never heard of Stone Valley.
I've got a couple of "beater" 36 cal Remingtons with pitted barrels, shallow rifling too, but they shoot fine. It is one of those things you do not tell other shooters about but must tell a new buyer. Now, I have not done precision accuracy tests. I only do Cowboy Action Shooting with mine.
SM means San Marco. I've got a few. Variable quality. My best serious match guns are a pair of ASM 44 cal '51 Navies I got back in 1994. Had a friend tune them and harden the triggers. They have been my best guns for CAS matches.
I recently read a posting where someone used Naval Jelly to remove the rust from a pitted ML rifle barrel and it shot pretty good afterward. He warned to not get Naval Jelly on bluing as it will strip it.
With over 15 perCUSSIN' revolvers, I've been called the Imelda Marcos of cap & ball.
SASS#3302 (Life), SASS Regulator, NRA (Life), DGB#129
Wolverton Mtn. Peacekeepers (WA), former Orygun Cowboy (Ranger, Posse from Hell)