You mean the firing pin? Maybe the IBoK might help:
From Iowegan's GP100 Book of Knowledge:
"Firing pin: Use a tool to push the firing pin all the way forward. You should feel the spring tension of the firing pin spring. Firing pin travel should be smooth. If not, force solvent into the firing pin hole and push the firing pin in multiple times to help clean out the firing pin and hole. Blow it out with compressed air. When pushed in all the way, the firing pin should protrude .055-.065”. This can be measured by laying gap gauge blades on the recoil shield and matching protrusion to thickness. The firing pin is secured by a recoil plate (part #31) and held in place by a recoil plate cross pin (part #66). Removing the firing pin is not recommended because it will damage the finish. The firing pin is a factory fitted part. To remove the firing pin, you must first drive the cross pin out then push the recoil plate (AKA firing pin bushing) from the rear. A coil spring (part #13) is installed between the collar on the firing pin and the recoil plate."