I understand that '03 Springfields suffer from slow lock-time due to a weak main spring.

Wolff offers replacements springs in 4 "strengths": 20, 24, 26 and 30 #. Which is best?

depends on the use,,, i believe the original is 18#, and the 20 or 24 is a good starting point!!

when you get heavier, it can be a bit hard to open!!!

jeffe

I agree with Jeffe, try one in the middle 20s.

The only time I would use a 30# spring is if the locktime is reduced by making the distance the firing pin travels less. This is a fairly complex modification and one that I can't see the merit in a hunting rifle. I have a couple that this was done on, but only because they had three position Win 70 style safties installed.

I have used the Timney model speedlock spring that Midway carries with good results also.