I realize hammer spring weight works in concert with recoil spring weight. The factory hammer spring weight in my 6946 is 20 lbs and the factory recoil spring weight is 15 lbs. If I go to an 18 lb hammer spring can I use a 17 lb recoil spring and keep the same ratio?

20 / 15 is a 4/3 ratio
if the hammer spring is 18 then , take 18 and divide it by 4 = 4.5
take 4.5 X 3 = 13.5 not 17 ... at least that was how we calculated ratio's in 1967 high school old math class...it may have changed , so much has .
Gary

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Certified Cajun
NRA Member

I guess I should have asked my question a different way. If I go from a 20 lb hammer spring to a 17 or 18 lb spring, what recoil spring would I use to keep from battering the gun?

Per your question, going on straight spring rate ratios isn't going to produce an equal result. The changes aren't linear. Secondly, while you're trying to keep the recoil forces the same, your proposed change is going to increase the forces of the slide going into battery. Which, are originally substantially more than the forces in recoil and resisted by the slide stop.

Exactly what are you trying to accomplish?

BTW, if you're trying to lighten the SA pull, the villain is probably machine marks on the sear/hammer and/or the sear spring.

This is a complicated subject and I am not an expert...

I would try to use the stock one and see how it works and check if I have any misfires.

As I understand, the less force on the hammer spring, the less force on the hammer to hit the primer, so there is a chance for light strikes and misfires. However, you may get enough force on the hammer and maybe you don't need to change a thing.

I am always concerned in using stronger recoil springs because of the extra force in the front of the slide, specially on aluminum frames.

There has been a lot of discussion on the Beretta forum regarding this subject. (of course on Beretta pistols that are different). There are people running much lighter hammer springs and using the same recoil spring. (Hammer spring Recoil spring ratio? - Beretta Forum)

Also, if I was going to change the recoil spring, I would check the space available vs. the size of the new spring to prevent spring binding. (Springs binding in my Shorty 45)

Hope this helps...

Thanks, fellas, those are all really good points to consider. Figuring S&W probably spent a lot of time and money on R&D, staying with factory spring rates and polishing machine marks is the safest bet.

If you're thinking about the interplay of hammer springs and rebound springs in revolvers affecting trigger pull, the first thing to point out is semi-autos don't work that way.

The recoil spring in a semi-auto is determined by the ammo you are shooting in that particular gun, not by your preference in recoil or by which trigger pull it has. It is chosen to make the gun work reliably without battering.

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Science plus Art

Excellent answer.

I have a similar combination in my 3914 & 3914DAO.

I run a lighter mainspring in many of my 3rd Gens & usually offset it with a slightly heavier recoil spring since the lighter mainspring will be exerting less initial resistance to the slide's rearward motion.

There's no real "ratio" between the two but the mainspring does help the recoil spring to a small degree until the slide gets over the hammer. After that it's all on the recoil spring.

I've done some home experiments measuring the change in force needed at different points in the action's movement & it's very measurable to see the change in force needed using different spring weights.

A 17# mainspring is the lightest I use in any of my 3rd Gens & I've never had a FTF issues related to a lighter mainspring.

If you're not shooting much (+)P ammo in it you could probably try a 16# recoil spring with it, if you wanted.

Remember to always thoroughly test fire your pistol after making any changes especially if it's to be used for self-defense.

.

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Waiting for the break of day