I have owned 5 of the S&W 45 ACP stainless self-loaders--3 of the 645s, 1 of the 4506s, and 1 of the 4516. In short, they are ungodly-strong, utterly reliable, will feed anything reasonably shaped for an autoloader, and are VERY lead-friendly. They had the poor fortune to get marketed right at the time of police department expansion into autopistol issuance and replacement of revolvers (mid-1980s) when SIG-Sauer went ALL-OUT to gain market share and Glock pistols came onstream. The 645/4506 were significantly heavier than the SIG and Glock products, and European pistols held (and still hold) a mystique all their own that seduces rangemasters and gunwriters like red-haired temptresses of easy virtue.
S&W metal-frame autopistols with 2-digit Model numbers (39, 59) are First Generation models. A 3-digit Model number (645, 459, 639) = 2nd generation model, of which the O/P's 645 is a member. The "4" prefix indicates aluminum frame material, a "5" prefix indicates carbon steel frame material, and the "6" prefix = stainless steel receiver. 3rd Generation S&W autos have 4-digit Model number, in which the first two numbers are the base caliber and series identifier, and the last 2 numbers are respectively sub-variant identifier and receiver metal identifier. IOW, my 4506 is a stainless original full-frame with 5" barrel. My 4516 is the compact version with 3.5" barrel and short frame butt.
The 645s had one mechanical flaw, and not a thing that any gun enthusiast should get all overworked about. The little ambidextrous safety/decocker lever on the pistol's right side (best used by lefties) on about 10% of the 645s would come unscrewed and fly off during firing strings. My 3 examples never had this occur, but when it happened I just kept a supply of new levers and screws on hand from S&W--put a drop of epoxy on the screw threads--and all was well afterward. But this little flaw REALLY got a few of our academy range staff's teeth on edge for some reason. The 3rd Generation S&Ws had a dovetailed right-side decock lever on the 4506 et al, so end of issue.
All 5 of my S&W 45 ACP barrels had grooves right at .451", and throats a few tenths larger. They digested .452" bullets with aplomb and without leading. They all ate SWC, TC, and RN castings without a bobble if you abided by Lyman bullet seating/OAL specs. The Lee 230 TC design seated with about .020" of front drive band exposed and given a mild taper crimp feeds wonderfully.
They have been fine service and hunting pistols for me since 1985. One of mine has at least 25,000 rounds through it, and has no wear issues. Their only negative elements were mentioned above--the decocker departures and overall weight of platform.
