Mainspring change in Model 66-5

[Recon]

I found a new and unused Wolff spring kit in my parts draw and decided to install it in my Model 66-5. The new Wolff spring in my Model 66-5 and its round butt doesn't appear to have anywhere near sufficient tension to fire despite the strain screw all the way in. It barely even dimpels the primer.

I've never had a problem with Wolff parts before but all of them were square butt K or N frames with the older firing pin system.

Has S&W changed something in the design of the action to cause this or do I need a new design of mainspring?

 

[tomcatt51]

I found a new and unused Wolff spring kit in my parts draw and decided to install it in my Model 66-5. The new Wolff spring in my Model 66-5 and its round butt doesn't appear to have anywhere near sufficient tension to fire despite the strain screw all the way in. It barely even dimpels the primer.

I've never had a problem with Wolff parts before but all of them were square butt K or N frames with the older firing pin system.

Has S&W changed something in the design of the action to cause this or do I need a new design of mainspring?

Sounds like you just need a longer strain screw. The Wolff springs work well but require a long enough strain screw. An 8-32 socket set screw works well and you can adjust the spring tension and loctite it in place. Some here disagree with this approach.

 

[Recon]

tomcatt51:

I think you may be right.

This revolver was a law enforcement trade-in even though it looked like it had never been fired. Also, it did seem like it had a lighter than normal double action pull. I simply assumed LE wouldn't modify their sidearms. I guess they probably did.

Regards...

 

[bountyhunter]

I found a new and unused Wolff spring kit in my parts draw and decided to install it in my Model 66-5. The new Wolff spring in my Model 66-5 and its round butt doesn't appear to have anywhere near sufficient tension to fire despite the strain screw all the way in. It barely even dimpels the primer.

I've never had a problem with Wolff parts before but all of them were square butt K or N frames with the older firing pin system.

Has S&W changed something in the design of the action to cause this or do I need a new design of mainspring?

+1 You need a new strain screw. If the mainspring hasn't been modified, it should work perfectly in a model 66 with a stock strain screw.

If you still have the stock mainspring, you could try it with the shortened strain screw as I suspect it was cut to work with a stock mainspring. A lot of people do this to reduce DA pull.

 

[HAWKEYE10]

I had a similar problem with my model 19. Found out
someone bent the main spring to make it lighter. The way
I found the problem was comparing that main spring
with one from another K frame. The main springs are
the same for a K-L-N frame. Hope this helps. Don

 

[Recon]

I compared the strain screw in my 66-5 to a stock one and it was ground off. The stock mainspring will work but if I choose to use the Wolff I'll have to use a new unmodified strain screw.