Hello Herman; great snag at the Mason show, M14's are some of the great ones. The differences between the M14 and M15 get a little confusing when it comes to some of the more esoteric editions, but generally, they are both k-frame, target sighted 38 spl. revolvers. M14's (K38 Target Masterpieces) typically have 6" bbl's and Patridge (...not Partridge, God forbid) front sights and are seldom seen in nickel (special order only, I believe; except of late). M15's (K38 Combat Masterpieces) typically have 4" bbls and ramped, Baughman front sights; also nickel editions are not uncommon. M15's were also made with 2" bbls,and much later (between 1986 and 1992) they were made with 6" and 8-3/8" bbls, at a time when S&W temporarily discontinued the M14 line. Confused yet? Well, a few M14's were also produced with special, un-tapered (heavy) 4" bbls with ramped front sights; these are as the Dayton guns and are pretty scarce. There are also reports of some 5" M14's. M14's were re-commenced in 1999. It takes the Standard Catalog of Smith & Wesson, 3rd Edition (abbreviated "SCSW3" around here), to be able to speak half-way intelligently about them, and even with that, you're likely to get into arguments (as well as interesting discussions) with other self-proclaimed experts on them. Bottom line: get thee a copy of SCSW3; it's cheap and readily available.
Now M16's are also k-framed, target revolvers, but are an altogether different animal, being that they are chambered in 32 S&W Long, and later (M16-4's) for 32 H&R Magnum cartridges. M16's (except for M16-4's) are scarcer than hens teeth, and get much respect (and big bucks) when they change hands. Why is that? Because they were originally very unpopular and nobody bought them; now they are considered to be rare. The M16 has the distinction of there being about twice as many old blue & gold boxes labeled for them on the market as there are guns. This, it was patiently explained to me, was due to a marketing error made back in the fifties. Anyway M16's are made in 4", 6" and 8-3/8" bbls and I've never even heard of one finished in nickel.
Now, I'll let some of the experts chime in here and add to this confusion. -S2