Darrel Holland makes a good one , its all steel and has been scaloped to drop weight this plus the higherpower spring makes for faster lock times.
Greg Tannel makes a pin and spring kit his pin is aluminum with a steel tip with a heaver spring , (I like this one the best) their is also a replacement bolt shroud kit he sells that is the complete pin spring and an new upgraded aluminum shroud , I don't think this kit comes with the light weight pin though.
David Tubbs also makes a pin and spring kit through "speed lock"
Wolff springs also makes heavier springs for the Rem 700's