In the past on some other sites I've seen folks vigorously proclaiming the virtues of one over the other and in some cases, sadly, the discussion degenerated into a virtual shouting match...which is both rude and in my view, stupid.
Let's just take a brief unemotional look at these revolvers and see if any conclusions can be drawn.
Both the 642 and 638 are intended to be snag free and for pocket or concealed carry. Both of these have aluminum alloy frames with the barrel and cylinder of stainless steel. Some parts are of hardchromed steel such as the triggers. Both are the same size and have round butt grip profiles. Obviously the primary difference is that the "hammerless" 642 does not allow single-action shooting while the 638 does offer that option.
This photograph better shows the differences between the internally hammered Model 642 vs. the shrouded Model 638. It's interesting to note that an "add on" part to shroud the hammer against snagging was once made for the Colt snubs that competed against the Model 638, so it would appear that concerns over hammer spurs snagging on clothing has been both widespread and long term.
One gun writer wrote that he has never been able to get any version of the shrouded J-frame snub to shoot as tightly as the others. Perhaps, but that has not proven true in my own experiences with both. I cannot shoot one better than the other in double-action. It seems to me that smoothness of the individual revolver's double-action might well be the determining factor should a fellow see much difference in the performance of two similar snubs from the same maker.
With the Model 638 the hammer can be cocked for a light, single-action shot if desired. To some the idea of being able to make a more precise shot, perhaps at distance, is an option that they like having. Others suggest that such is not at all likely and that the single-action option leaves one open to suggestions during a civil suit that they cocked the revolver and then unintentionally and negligently shot the poor scum that was trying rape, rob, murder, (take your pick) them. I
suggest that the buyer/owner/shooter make his decision on which to get based on his own perceptions of what is important.
Lowering the hammer on the Model 638 is done with less thumb contact on the exposed portion of the hammer spur. I have never had a problem with it and I do not think that it invokes any major difficulties over lowering a non-shrouded hammer, but I don't think that it is quite as "sure" on the Model 638.
Some years ago I read that if carrying the Model 38 or any version of the shrouded snub to be sure and not have any loose change in your pocket or a dime could become wedged between the hammer spur and the frame and tie up the gun. Unless S&W has altered some dimensions on the hammer or frame, I found this to be impossible to do. A dime simply will not fit between the side of this revolver's hammer and frame. I guess a paperclip or an object of the right size might could do this, but a pocket holster goes a long way in preventing such. I also carry only the holstered revolver in my pocket and I'll bet most other folks using this method of carry do the same. I have found
the area behind the hammer on the 638 to be a "lint & crud magnet." Pocket carry is simply dirtier than most expect and after toting the Model 638 for ten days as I normally do my well-worn Model 642, I was surprised at the amount of crud that it had picked up. At the same time, the gun worked fine and the trigger pull was not affected.
For me, the Model 642 is the favorite.
The primary reason is the lack of another opening for grit and lint to build up. That is my "primary reason", but it is not much of one if we simply clean and maintain our personal carry guns at least once every week or so. Being an old revolver guy for years, I shoot primarily double-action with most six and five-guns and do not find the single-action capability on a revolver of this size to be that much of an advantage. (I definitely do prefer having a single-action option on K, L, and N-frames.)
In the end I simply cannot find much difference between these revolvers in practical terms. One may have a bit of an advantage in some aspects while the other offers what
might be a plus for some people.
"Beauty is in the eye of the beholder" and is subjective, but I find the 642 more pleasing to the eye. Some will agree. Some will not and others won't care one way or the other, but it is my opinion that either of these little guns will serve about as well as the other and that the potential buyer/user should go with the one he/she prefers.
I just don't see much difference between these two revolvers and were I in the market for such a snub, I'd probably go with the one having the best price or action.
Best.
