I received a review holster for the S&W 629; even using the kit for breaking in the holster (to make sure you get a tight fit while allowing for slight manufacturing tolerances), the thumb break will not snap. We are not talking a small difference but many tenths of an inch. Even gently tapping with my plastic headed gunsmithing mallet is not going to solve this. It strikes me that my 629 has an adjustable rear sight that looks like it could be the reason for failure to seat. I believe fixed rear sight 629s are quite rare, usually special order 3" barrel versions, for those of you not getting enough daily handweb abuse. Any other guesses?
This is a tight enough fit that I do not see it as a big deal: I am not going to carry this beast except if hiking in grizzly bear territory (which really never happens), or when running to the store during a Zombie Apocalypse (which is slightly less likely). If I ever live somewhere that requires concealed carry of a .44 Magnum, it is time to move (perhaps off-planet). I also do not see myself running or jumping fences with this mass of beautiful stainless steel on my belt, either. The snap break is just not needed. I am just trying to figure out: Why?