OT, I understand that the P-64 was originally made to shoot much lighter bullets then what we use here and at the same velocity, about 20 grains lighter and with a very hard primer. You can use the stock springs but I changed the original 17 lb recoil spring to a 22 lb. so the little gun takes less battering by the heavier recoil of present ammo. The stock hammer spring is well over 20 lbs., double action shooting with that is nearly impossible. I swapped that for a 18 lb. hammer spring which is still heavy but is doable. The gun operates fine after the spring change, I believe that I will never have to change them again.