I am a Pachmayr rubber grip fan. I have a house full of revolvers and nearly all of them have Pachmayr's on them. They are bone ugly but "Pretty is as pretty does" and they DOES!
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I have a 624 4" and while it is chambered for the .44 Special, it is essentially the same revolver as your anticipated Mountain Gun. It is noticeably easier to pack than the regular 629 4". It also seems to handle better. I use mine with the "Skeeter" load, which is 7.5 grs of Unique behind a Keith 240-250 gr (Lyman 429421). It is a really good combination.
Incidentally, it is also a good small game load. I have killed a number of snowshoe rabbits with it. Mostly, would jump them when grouse hunting. They would get up and run about 25 yards then stop and look to see what I was doing. What I was doing was tucking my shotgun between my knees, drawing my revolver, and as soon as they stopped slip a Keith bullet "through the slats". High percentage shot, and no meat damage. My family just loved rabbits with no shot in them. You DID have to be ready for them to stop as they would only wait a few seconds.
Good luck with your mountain gun.
Dale53