I bought the Wolff springs for my shooters (.30 cal and 9mm). Even though they state their springs are for either cal, the lighter spring is still too strong for the .30. Saw a post here once (think it was from LugerDoc) stating that you had to remove 2 coils from a spring for it to work in the .30. I just kept the original spring that came in my .30 and it shoots 93gr FMJ Fiocchi through MecGar mags just fine (yes, that is my ammo on the trader board). Thanks for the plug Don.