I have a custom shop Springfield - and it has a 9 lb spring. He told me to break the gun in and then try to up it.
I ordered a 12lb and 14lb spring. I tried the 12 lb, and it would not work right, so I didn't even bother with the 14 lb. I went back to the 9lb, and all is 100%.
Now, I have ordered a new 9lb and 10lb, which will be here Mon. I will give the 10lb a shot. The gun is fit VERY tight.
Anyway, my point is that you may have to try a couple of different springs if ya don't already know what's in the gun now.