You can take that lock out entirely and it makes zero difference. That was a CYA from SIG . The FRT15 SIG conversion is common these days and its not illegal. The trip bar from parker is not a full auto conversion. It just link the trigger to the carrier the same way an M16 carrier works in an FRT15 equipped AR. The firing pin lock on the MCX is truly unnecessary. Firing the gun without it does not cause it to chain fire. Its just like firing an AR without a firing pin lock.