Well, there was the Colt Officers ACP
Some wandering observations . . .
The OACP arrived with a six-shot magazine, because the frame was one round shorrter than the standard Colt's O-frame. Later on, both the standard seven shot mag body and the shorter one benefitted (?) from the advent of the Shooting Star type follower. Point is, the OACP frame WAS shorter.
In general, the pistols with the shorter frames tend to be made in much shorter barrel and slide lengths, with attendant problems in timing and reliability. I count myself very lucky to have a lightewight OACP which functions consistently. In general, anything much shorter than the Commander length (4-1/4") barrel are pretty finicky. Kimber has produced some 4" guns that work most of the time, but I have no personal experience with the others.
For my own use, I am astisfied with the standard Commander dimensions. The butt length is, indeed, more of a factor in concealment than slide length. Colt produced a variant - - I think it was called the Concealed Carry Officers - - With a Commander slide and barrel fitted to an OACP frame. Problem ws, it
looked out of proportion. Let's face it, aesthetic appeal IS a factor, and many buyers can't get past the appearence of a particular model, no matter how efficient and practical the design.
I imagine it is practical to produce a .45 autopistol with a five shot magazine. You'd still be facing reliabliity problems, going below a four-inch barrel.
Let's face it - - If one wishes the advantages of the .45 ACP cartridge, one gives up a degree of concealability. It is NOT a proper cartridge for a true pocket pistol - - Not with modern clothing designs. If one needs a true pocket pistol there are some very small ones in 9x19mm -- regardless of it's limitations, this is a decent small pistol cartridge.
Best,
Johnny