The same dilemma when I setup my Stock 2 because I shoot IPSC Production. The lightest hammer spring you can use with factory firing pin is 14 lbs but you have to use exclusively Federal Primers. Others like CCI, Winchester, Magtech, will not se toff.
I have no problem with it until Federal became difficult to find here in the Philippines. So we were forced to manufacture extended firing pin as long as the EGW but can still retain the FP block.
Get an extended FP and no problem with any primer. Now I use CCI.
Since you can't reload use Federal Ammo exclusively.
Hope this help.