I used the Wolff springs for a P-12 magazine. They reduced the capacity from 10 to 9 but the one round trade-off was worth having working magazines. Never had a feed issue after installing those springs. I did not attept to trim them. From Wolff's site:
MAGAZINE SPRINGS are available in +10% extra power to assure proper feeding.
For use in:
P-12, 12 round magazines
10 round Para magazines - all calibers
Stock No. 76471 +10% XP - each.....$ 7.49
Stock No. 76473 +10% XP - pak of 3.......$ 17.29
Stock No. 76474 +10% XP - pak of 10.....$ 47.99