You can download the SW99 series owner manual from the archived section on this page.
Owner's Manuals - Smith & Wesson It will describe the operation of each model.
The standard SW99 was essentially the Walther AS.
The SW99 QA would have been similar to the Walther P99 QA, in which the striker is partially pre-cocked when the slide is retracted (like when chambering a round), and then the trigger completes the process of fully cocking and releasing the striker to fire the gun. The pre-cocked striker in the QA is released via a field-stripping button located in the slide (same location as the AS decocking button, but smaller).
The SW990 would have been the DAO model. (Like the original P99 DAO was first called the P990)
The SW990L was a unique model for S&W, with the smooth slide of the DAO, but the trigger/sear action of the QA. We were told in one of the armorer classes that the "L" was tentatively going to stand for "Lightning", for the short & fast trigger of the QA sear action. The 990L's partially-cocked striker had to be released for field-stripping the gun by pulling the trigger on an empty chamber (like the Sigma). It lacked the field-stripping button on the slide of the Walther QA model.
The SW99NJ was a very limited run of guns, and one of my armorer manuals was printed to include info about it after that model had been produced (I think it was at the time of my second class), since it differed slightly from the regular model (at the request of the NJSP ... which is another story in itself
). I've wondered if that armorer manual listing the SW99NJ model might become a collector piece among armorers.
Now, while S&W originally planned to release QA & DAO models, I never saw any of them myself. I rather wonder if they ever saw production. The only models used in the armorer classes I attended over the years were the standard AS-type guns.
There are some minor differences among the models/calibers, but those are only important to an armorer/repair tech, as they aren't anything an owner would normally be concerned with for normal field-stripping & cleaning. Different sear blocks; different trigger bar guides (although there's actually a range of them listed in the German tech/armorer manual, in case a particular gun has a "timing" issue regarding striker travel distance and the release point of the striker in DA mode); trigger bars; a couple of extractor springs; extractors; a couple of striker springs (standard/AS v. QA/990L): a couple slide stop lever springs: different locking blocks in the full-size & compact models ... just off the top of my head.
The bottom line is that the SW99/990L series were pretty good pistols, like the Walther models. Just different slide & barrel manufacture.
