This is from "Survivor's SKS Boards":
New Hammer Springs...updated (misfires cured!)
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on: March 30, 2012, 04:48:15 PM »
After many reports of misfires with an all original set-up, and then reports of misfires when using our Firing Pin & Spring, we had Wolff manufacture some special Hammer Springs for us. We had hoped that when the trigger group was properly tuned, the lightest, (Wolff's original 27.5 lb hammer spring) would be adequate to provide consistent ignition. But our testing, and our customers reports are indicating that if you use Berdan primed ammo, (Wolf mostly) you are going to need a stronger Hammer Spring. And we have it. It is rated at 31 lb, (34 lb being factory original strength) and it is doing a great job at providing that very near 100% ignition while allowing a better felt trigger pull.
Until we get them listed on our shopping cart, you can call our toll-free order line to get yours. Available seperately for $8.00, or with a Wolff "Reduced Power Sear Spring" included for $9.00. (+$2.00 shppg if total order is under $11.00)
866-232-4867
You can get more details and read how we incorporate them when installing our Made in USA 922r Compliant Hammers, Sears, and Triggers, on this page of our site:
http://murraysguns.com/922r.htm
Many original hammer springs have taken a set over the last 40 to 50 years, and we've seen quite a few tr groups with an unidentified replacement hammer spring that was obviously too weak. So if consistent igniton is a problem for you, try our 31 lb spring, or for an extremely stubborn gun, you can order the 34 lb "original" strength spring.
If you shoot exclusively Boxer primed ammo, the 27.5 lb Hammer Spring is adequate to ignite primers consistently.
Note: Wolff= Wolff Gunspring Mfg Co
Wolf= Russian ammo supplier