Hello Glockbox
The model 645 was the very first S&W Pistol to be chambered in .45 ACP. It was made from 1985-1988. There were some Proto-Types released to Factory employees and those had Investment Cast receivers. They are rare and the Last one auctioned went for an alarming price of $67,000.00 as it was and engraved Olympics model. The first 25 were engraved and command this premium price. 100 were made in the Cast receiver Proto-Type models. These were done as an endurance test run and S&W then decided to make the factory run guns with Forged cast receivers after this. The serial range for the 100 Proto-Types was A8833XX to A87XXXX. If you have one in that serial range it is a very valuable Pistol.. Regards, Hammerdown