I've replied and posted within a number of Searchable thread topics on the SW99/P99 pistols on this forum in recent years.
I own a SW9940 (standard size .40) and a SW999c (compact 9), both of which are what would be called AS (Anti-Stress) mode 99's by Walther. Carried an issued one for a few years, and as a LE firearms instructor, logging many thousands of rounds downrange through it (and mine).
The 99's have benefited from a number of revisions and refinements over the years, some of which are more obvious (cosmetic) and some of which aren't easily seen by someone not familiar with the workings of the guns. At least a couple of these revisions mean that some parts (like the sear housing block assembly) are not "interchangeable" between older and newer models. A change in the shape and size of the SHB body was one change (requiring a corresponding change in the inner design of the frame), and then when Walther engineers later changed the trigger bar guide from a post, to an "adjustable" lever. The SHB and the frame were changed to accommodate this revision.
Early in their partnership with Walther, S&W engineers identified a problem with the .40's, which was an infrequent and unpredictable occurrence of early slide lock back (with rounds remaining in the magazine). We were told (in one of the armorer classes) that after careful study of different aspects of the gun, S&W high speed imaging revealed that sometimes recoil might cause a lateral wiggle/displacement of the top rounds in the mag, which might hit the slide stop's inside tab and cause the slide stop to engage the slide's stop notch, locking the slide back with rounds still in the magazine. They told us that once this information was passed along to Walther, it was subsequently resolved by Walther having Mec-Gar make a change to the magazine bodies (and the followers required a revision because of the change in the mag body). Problem solved. (This wasn't an issue with the 9mm guns, or the later SW9945 & SW990L45, BTW.)
The 99 series was, and is, an excellent pistol in many respects, and certainly one which deserved more attention than it received. I remember S&W putting some full page ads in some gun magazines in the early 2000's, but it wasn't being pitched very hard against their primary 3rd gen pistols, which were selling well, but becoming increasingly expensive compared to plastic guns.
I was told that as the end of the 13 year Strategic Alliance between Walther and S&W was coming due to expire, both companies were looking to go in different directions. Walther finally decided to open its own importer in the US, and S&W had been involved in a secret 4 year project to design a new "flagship" plastic pistol line of their own, making some substantial changes to the plastic pistol frame concept.
They also introduced a mid-priced plastic pistol line, intended only for commercial sales (the SD), which would have a price point between the Sigma and the new M&P. They eventually decided that having 3 separate plastic pistol lines was a bit much (and probably confusing to the public), so they more or less folded the Sigma and SD together, making a new budget line for the frugal buyers just looking for a standard single-size plastic pistol available in either 9 or .40, and put their attention to the expanding the higher end M&P.
Walther has been making more of a footprint in the US, but it remains to be seen how aggressively they'll go after share of the lucrative US market. It might even be interesting to see if they stick their toe in the American LE market share.
In this new age of "one consistent trigger pull" marketing, the ability of the handgunners of yesteryear to operate both a DA and SA trigger of a revolver, and then the DA & SA trigger modes in the "traditional double action" pistols which entered LE and military use in earlier decades, seems to have fallen by the wayside. (Traditional Double Action, or TDA, for short, is the formal name for what's usually known as DA/SA among gun owners.)
I've sometimes heard the TDA pistols referred to as "the thinking man's gun", usually meaning the more skilled and experienced shooter (who isn't a 1911 user, which is another dedicated "group"
), long after Cooper nicknamed the TDA guns as "Crunchentickers". Potato, Potahtoe ...
If someone likes a TDA pistol, the AS version of the 99 series offers an excellent variation, with very smooth and consistent trigger pulls in both modes.
I won't put the rest of my experiences as an owner, users and armorer for the SW99/P99 in this thread, but you can look for the older threads and browse them, easily enough.
