Many of you probably know this already, but for those who don't
Normally when using a shim to open a padlock you want to get it turned all the way around to the inside of the shackle. However this sometimes just doesn't work and with locks that have strong springs may even break your shim.
In cases like this try a more side rear attack on the lock wiht you shim. Turn the shim just past 90 degrees untill it meets resistance and then trying shiming at that point.
Seems to work best on combination locks