I note on the Wolff website that the 3953 factory spring weight is listed as either 17 pounds or 20 pounds (both with the short springs). One of the 10xx series is listed as using short or long springs. There were other such variations.
How sensitive are these guns to hammer spring weight? First, and most important, in reliable ignition and next in the affect this has on trigger return and trigger pull. Any expert knowledge out there?

I believe the Wolff brand 17 lb springs listed are designated for the DAO model numbers only....noted with a asterix in the list. The "short" Wolff springs are all approx. the same length. The difference in weight appears to be from a slight difference in the size of the wire used to make the springs.....with diameters measuring from approx. .046" - .050".

Although the lighter/heavier spring weights don't effect the trigger return as you would experience in a revolver, for instance, all spring modifications are a trade off of sorts. Installation of lighter weight hammer springs obviously reduces the trigger pull weight on the DAO pistols, but often results in a greater likelyhood of misfires due to light primer strikes. For this reason, most shooters rightly believe it's best to retain the OEM spring weights in duty or carry guns. Reloaded ammo and lack of maintenance also add to the variables.

Also, don't forget about the roll the mainspring plays in the actual cycle of the pistol itself. Lighter mainsprings (and recoil springs) have a direct affect on the firing cycle, and modification of the springs to a lighter weight can cause cycling, feeding, extraction and ejection reliability issues, and can also contribute to unnecessary battering of the frame and other components.

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Ret. LE, FA Instr, S&W Armorer

Thanks for the info, good stuff. Other than just general inquisitiveness, I'm an all DAO guy in 3rd gen Smiths. I find it interesting S&W shipped 3953s with either 17 or 20 lb springs. It would seem to indicate that they were tolerant of a wide range of weights.

I don't think the DAO's were shipped with either 17 or 20 lb. OEM mainsprings.

Perhaps I'm wrong, but the way I'm interpreting Wolff's info on the web site, according to Wolff's research at least, the "short spring" DAO guns were 17lbs, and the "short spring" DA/SA variants, like the 6906 for instance, were 20 lbs.

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Ret. LE, FA Instr, S&W Armorer