Grayfox and Jeff Thomas--re holsters for the S&W Mountain Gun. I notice that the latest (12/99) catalog from Dillon (1-800-762-3845) contains two holsters made specifically for this model: a Kramer Belt Scabbard (p.29) and a Kramer Vertical Scabbard (p. 53). The Vertical Scabbard has been available from Dillon before for the 5-inch full-lugged N-frame, but I believe that this is the first time it's also been offered for the 4-inch Mountain Gun. The holsters are $58 each.
As far as my own purchase of a 629 Mountain Gun is concerned, I went back to the dealer to look at the gun again. Perhaps not surprisingly, it was still there. The dealer freely admitted that the previous owner traded it in because he couldn't tolerate the recoil with full magnum loads. Also, he offered to lower the price to $469, which would help a little. The gun is in good shape--no mars or scars, well timed, good trigger. Barrel-cylinder gap is at the high end of the normal range (.008--I had a feeler gauge with me). The rear sight was adjusted all the way up--I can't figure out why, so this concerns me somewhat.
The posts in this thread have all been excellent and informative, and I'd like to thank each of you for responding. After reading these posts, I figure the Mountain Gun is a useful concept, but can be problematic in .44 Magnum. Apparently, the weight saved by the lighter barrel would be important mainly to a backpacker paring his burden to the last ounce. The 625, 657, and 686 Mountain Guns sound like good alternatives. Fubsy's comment about the grips is also appreciated.
Based on these posts, if I were to get the 629, I believe I'd see it primarily as a .44 Special, but with a .44 Magnum option. G. Kennedy's suggestion of shooting Remington medium velocity magnums looks like an effective compromise.
Anyway, thanks again.