Here's how I've done mine. Remove the barrel and trigger. Restrain the trigger spring as you remove the trigger as it will fly off someplace and be hard to find. Install the breechblock/hammer assembly breechblock first into the frame. Install the screw in the breechblock. Then reaching thru the trigger hole with a screwdriver or similar tool you can maneuver the hammer into postion to install the screw. Once it's in place reinstall the trigger and barrel. This has worked for me. If it is a replacement spring make sure it is not too long or the hammer won't go into position. I hope this helps.