Wolff has heavy duty springs that will replace the outer spring in a dual recoil spring set-up.
I use them in my 4013 single stack to 10mm conversions.
Please read the thread:
1013/4013 Here it is, history in the making & 4516-1, -2, 4536 and 457 in 10 m.m.
Wolff #477XX, I use a 47723 in my 4013/10mm and a factory stock inner.
See pictures in post #1.
•Reduced Power...: 15 Lb.
•Factory Standard.: 16 Lb.
•Extra Power........: 17, 19, 21 & 23 Lb.
See post #45 for the dual spring conversion.
S&W will not sell you a bushing to utilize the smaller guide rod with the dual spring.
That was done to use up existing slides with the bigger hole in them when they made a revision change to the spring design.
And also updated, only if the gun was returned to the factory for a repair.
I have made some for a few people that wanted to go with the dual spring-heavy duty set up.
I have a few more left and a longer guide rod was still available a little while ago, it just had to be shortened.
Regards,
BM1