Automatic Improvement Program!
Frankly, hooksnatcher I'm astounded no one has seen fit to comment on your pistol!
The AIP (Automatic Improvement Program) pistols were literally the 3rd generation S&W pistols aborning!
Pre-production prototypes is what some folks have called them.
Smith & Wesson was testing the manufacturing and utility of design changes inspired by efforts to refine the existing product.
For example, everyone knows the 3rd gens went to the one piece delrin grip.
But what most people don't know is that S&W straightened the grip angle two degrees on the 5906 from the 659.
Two degrees?
Why bother?
I've never heard the official reason although I suspect it had something to do with the first shot double action trigger squeeze pulling the sights off target with the straight back grips on the 659 while the curved grip as installed on the 5906 seemed to mitigate that problem. And straightening the grip angle accommodated the now longer front to back length of an already too wide grip. That's my guess, anyway.
I digress.
Out of a run of pistols that sold in the hundreds of thousands (possibly millions, I don't know total 3rd gen production numbers) yours was one of the first 528 built.
BTW S&W used the AIP serial number prefix on all its pre-production prototype models (5904, 6906, 6904, etc.) and not just the 5906. Consequently, your 5906 could be much earlier than number 528 in 5906 production. In actuality, it may have been one of the first 100 Model 5906 pistols ever built!
I hope others chime in on this fascinatingly brief but essential period of 3rd gen history.
If you haven't already, access the search function on this forum and Google custom search: "AIP" and "Automatic Improvement Program". There are a number of interesting posts.
Neat pistol!
John
