There’s a condition that can occur with some stock Colt SAA’s that I call the “Locked Up” condition. This is where the hammer is ¾’s of the way down but not all the way and will not cock back or go forward to the frame. This situation is most common in 2nd and 3rd generation Colt’s. It’s actually caused by improper tuning during the assembly processes at the factory. It seems to occur on about 70% of the post war Peacemakers I work on. It’s one of the issues we address when performing our Gunslinger Deluxe Action Jobs. But for now let’s assume you have a stock Peacemaker and find yourself with this problem. The reason your Colt is locked up, is that your finger ever so slightly let off on the trigger while you were lowering the hammer from the full cock position after loading or unloading your Colt. The way to avoid this condition is to simply make sure you hold the trigger ALL the way back with your trigger finger until the hammer is ALL the way forward against the frame.
If you have done things incorrectly and find yourself in this “Locked Up” condition, here’s how to correct it. First you will notice that the hammer will no longer go forward or backwards.

To “Unlock” your Colt, first gently pull the hammer back until it stops.It will only go back a very small amount before you feel it stop. Hold the hammer back against this stopped position, then pull the trigger again and hold it Fully to the rear. This will let you release the hammer and lower it down ALL the way to the frame. Your Colt is now “Unlocked” and should function normally again. If your Colt does not respond to this solution it may be broken or damaged and should be examined by a qualified gunsmith before further operation.