The L-frames were S&W's response to the issue of K-frames not standing up well to a steady diet of full-house .357 magnums. When Bill Jordan and others encouraged Smith to bring out a K-frame in .357 the idea was to practice with .38's and reserve the magnums for zeroing and duty. Towards the end of the revolver era in law enforcement more agencies adopted the philosophy of "train like you fight," and began to do so with magnum ammunition. This led to recurrent end shake issues with the K frames as well as a few split forcing cones and other problems. The L-frame addressed these issues, and became the last and arguably the best of the duty revolvers before that industry stampeded to semi-autos. S&W offered them in various barrel lengths, with the 4" the most popular among most officers, in blue and stainless (with the latter being vastly more popular for ease of maintenance), and in fixed and adjustable sights (with the latter far outselling the former). IMHO the 681 is perhaps the most business-like, even sinister, of the whole marvelous family. I believe the 681 (and the even rarer 581) will increase in value faster than their adjustable-sight counterparts. As is so often the case in the firearms world the rarer items become more desirable to collectors; they are rarer because they didn't make as many; they didn't make as many because they weren't as popular. Rich irony. As an armorer for a thousand-man agency in the PNW in the 70's and 80's I can tell you we continually and regularly had to deal with end-shake and timing issues with K-frames, marvelous though they are, even shooting only .38's (though in fairness, we shot a lot). The L-frames, N-frames (and Ruger -Six series) rarely suffered in that way.