Hoping "Fastbolt" will jump in. opinion on the 17 spring in the 6906. It dose make a big difference in the fell of the trigger pull (like the Beretta 92/96 D-Mode) difference. Will try Wolf and Tula ammo ( supposedly hard primers ) to make sure of the reliability of the Hammer spring. Did qualify on my 4006 after changing the hammer spring. Send thoughts and experience, I would appreciate it.

The mainspring plays a roll not only in the efficacy of the hammer strike, but also in providing the required resistance to the forces imposed by detonation and subsequent rearward movement of the slide on the frame. Without this calculated and required resistance, the pistol can suffer damage, and reliability may be compromised. This resulting damage is particularly evident on guns like the 6906, which has an aluminum alloy frame.

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Ret. LE, FA Instr, S&W Armorer

I agree with armorer 951. The mainspring does have an effect in the slide's cycling.

There was a time when I was experimenting with the use of a slightly lighter mainspring in a 6906. I ended up using the 19lb reduce power mainspring offered by Wolff for a while, but eventually returned to using the slightly heavier stock mainspring. Ditto trying an extra power recoil spring in the same 6906 for a while (trying to balance the recoil spring rate change with the mainspring rate change).

I never had a problem with the 19lb spring igniting primers, but then I only used the factory duty ammo we stocked, and as an armorer I kept the firing pin channel of my 6906 meticulously clean.

The trouble was that as other of our people sometimes used excessive amounts of solvent and CLP's on their guns (cleaning their weapons like some people wash cars), the firing pin channels over time often acquired excessive fouling inside the firing pin channels (and bits of brass shavings from case rims and primer cups), and then even the stout factory mainsprings would produce insufficient force to ignite primers. Now, factor in a reduced power mainspring and consider how it might affect things under similar conditions.

Some people have said that the factory mainsprings in S&W 3rd gen's are strong enough to push firing pins to break rocks, but there's a reason for that, and the reason is being able to produce sufficient power to reliably ignite primers under less-than-ideal conditions (should they occur). Hard primers, heavy fouling and unexpected contamination (submersion, or migration of for example) and fouling are a couple of less-than-ideal conditions.

Sure, there have been some times when the factory reportedly used lighter mainsprings on some of the DAO guns, but that was a long time ago, and it didn't spread to incorporate the stock TDA guns.

Now, it may be another matter if someone is putting together a target/game gun and wants to adjust the gun's functioning to their "individual requirements", and they aren't planning to rely upon it for dedicated defensive use, and they don't mind if the changing of spring rates may affect reliability and perhaps long term wear & tear.

As a LE armorer my only concern was to try and keep the guns, both issued and personally-owned, in original condition to try and maintain optimal reliability for defensive use. I saw LOTS of issued and personally-owned cop guns that were subjected to abusive conditions, as well as user/owner "maintenance abuse", ranging from both the "neglect" and the "over cleaning" ends of the spectrum.

You know what made the most significant difference in the shooting my my issued 6906's? Installing the 1-piece Hogue wraparound grips w/finger grooves. Gave me the optimal trigger reach (which has a lot to do with execution of trigger pull technique), as well as recoil management. Adds "meat" the grip dimensions, sure, but I really liked them for the live-fire benefits. Again, for me. I have them on my 4013TSW, comes to that. They can sometimes require a little attention and adjustment to get the hard plastic insert tabs to slip over and fit in the frame cuts on the back of the grip frame, though. I found my jeweler's needle files to be handy for that.

Just my thoughts.

BTW OP, I noticed you tried to PM me and my mailbox was full. That happens virtually every week. I can't seem to keep it cleared. Sorry.

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Ret LE Firearms inst & armorer

Armorer 951 said it well. The job of the mainspring is not just for powering the firing pin, but it provides resistance to the initial movement of the slide during recoil, delaying the unlocking of the breech. A lighter main spring will allow the slide to move backward quicker and speed up the unlocking of the breech, which can cause peening of impact surfaces.

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VCDL, GOA, NRA

The 6944 / 6946 uses a 17lbs hammer spring as a factory standard and it is built on a 6906 frame. I shoot it at qual time.
and some at the range. It is my summer carry "off-duty" gun.
opps (retired now). Thanks for your answers. I'll stock up on more springs when I'm done moving. Don't think a pound of pressure one way or the other would make a difference??? Be Safe.

Not according to the 2012 S&W Pistol Parts List for 3rd Gens.

PN# 069740000 (20# mainspring) is standard in (33) different 3rd Gens which include all the 69xx pistols.

I have used the 19# thru 17# mainsprings in various 3rd Gens without issues. I usually offset it's reduction in strength with an increase of a couple pounds in the recoil spring's strength, as has been mentioned.

While I've never had any issues with FTF in any of my 3rd Gens they are primarily casual use pistols.

The ones used for SD carry have factory standard strength springs in them, just to be safe.

If you did use the lighter springs in a SD carry pistol I'd test it extensively before carrying, keep it cleaned/lubed, & with fresh springs, again just to be safe.

.

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Waiting for the break of day

The Wolff Gunsprings company listed that bit of info on their website (at least last time I looked). While I've never heard it recommended by S&W in the 4 armorer classes I took for the metal 3rd gen pistols, I'd not rule out the company having made a short run of their older DAO compact 9's with a lighter mainspring, or if a customer agency had requested it. Never say never with S&W.

I'd have to go through some boxes to find my late 90's Parts list (binder hardcopy), but the oldest digital Parts lists I have only show the standard compact mainspring. Again, never say never with those engineers.

I tried the compact 19lb mainspring in one of my 6906's for a while (approved by the then-head armorer). Nice DA trigger pull. I eventually changed it back to the factory spring, though. It was my primary duty weapon at the time. The potential for a really hard primer (BTDT) to come under the hammer, or something happening that exposes the gun to harsh environmental conditions at just the wrong time (which might interfere with hammer fall) made me want to go back to using the factory spring.

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Ret LE Firearms inst & armorer