The Semmerling LM4 has pretty much no historical significance, but it does have a pretty unusual operating system. It is a .45ACP backup pistol developed by a fellow named Philip R. Lichtman in the 1970s. It was a pretty compact pistol, intended as a last-ditch backup weapon while still being in a major caliber. Lichtman’s trick for getting a 4+1 capacity .45ACP into a small package was to make it a manually-operated gun instead of a semiauto.
The LM4 has a slide, but instead of cycling backwards it cycles forward (similar to the Schwarzlose 1908), and the shooter must cycle it manually. This allows the design to get by without many of the components necessary for a self-loading action, thus allowing it to be smaller than the other repeating guns available at the time. In theory, fewer parts would also lead to a less expensive gun, but the LM4 was quite expensive ($750 or so retail in the late 70s/early 80s). The whole gun was made out of extremely high quality tool steels, when lower grade materials would have worked just fine for many parts. Only a few hundred were originally made, in part because of the high cost. The other reason for the gun’s commercial failure was, to be blunt, the fact that it was a pretty lousy gun in practical terms.
Now, I should say that I am basing this assessment on the current-production LM4 as manufactured by American Derringer – I have not had the chance to try out one of the originals. But the American Derringer version leaves an awful lot to be desired. The magazine is held in the gun by two bent tabs at its base, which have a tendency to jolt loose on recoil – which is pretty hefty, as you would expect. The manual action is pretty finicky, and you have to run the slide briskly and with the right technique to successfully eject an empty case and chamber a new round. Worse, the slide is shorter than most folks’ hands, and it is very easy to unintentionally let your pinky finger wander in front of the muzzle while cycling the pistol. I suspect that if a large number of these were actually ever used in defensive shootings, there would be a frightening number of self-inflicted wounds when people were trying to shoot and cycle the action under stress.
As if it needed any more bad news, the LM4 is simply obsolete today. There are several 9mm semiauto hideout pistols being made today that are the same size and a good deal lighter than the Semmerling (which comes in at a surprisingly hefty 24oz). Anyone who is dead set on a .45 has the choice today of a new AMT Backup, or realizing that a reliable 9mm is much more useful that a .45 that you are liable to blow your own finger off with (or getting one of the DoubleTap modern derringers that are just coming onto the market).
For you sci-fi enthusiasts, you may recognize the LM4 from its use in F. Paul Wilson’s Repairman Jack series of novels. I really enjoy the stories and Jack’s character, but the Semmerling was really a pretty poor firearm choice for him. But hey, it’s fiction.