Remington-Pedersen .45acp Model 53.
Here’s a neat one. Many firearms enthusiasts are aware of Pedersen’s Remington Model 51, widely considered to be one of the finer (if mechanically complicated) pocket pistols, being very accurate, pleasant to shoot and extremely ergonomic. It’s method of operation was not simple blow-back, but rather “hesitation” lock or action:
"During firing, the cartridge case is set back about .08" by chamber pressure. This starts the rearward movement of the breechbolt and slide. The breechbolt engages a shoulder on the frame after having traveled about 3/32". The slide continues rearward, lifts the breechbolt out of its temporary engagement, and continues to compress the action spring."
While it was later recognized that a locking action was unnecessary for the .380 and smaller pistol rounds, relatively few people know that a .45acp prototype was built for testing by the Navy as a potential replacement for the 1911. Reports indicate that with its fixed-barrel and low bore axis, the .45 Remington-Pedersen Model 53 outperformed the 1911 in just about all areas and was tentatively chosen, however a sudden entrance into WWI made it so that the already tooled-up 1911 continued being produced and the Model 53 fell by the wayside.
Considering the continued acceptance of the 1911, perhaps this model, if reintroduced, would prove to be as much of a success in the civilian market as it apparently was with the Navy.
See more at http://www.forgottenweapons.com/remington-m53/