The mainspring vise is the best and proper way to disassemble it, and any lock for that matter.
In the factory for repair, a simple modified pliers was often the bench tool.
Locks were disassemble and re-assembled many,many times in the course of a stubborn repair.
Smooth jaws, sometimes braze added and smoothed out so as not to mark the spring or sear edges.
A small piece of leather sometimes used as well.
With the lock in the fired position,,
Grasp the bottom of the sear and the top of the mainspring up as close to the bridle as you can and compress.
It helps to loosen the bridle screws before you do this so you are not struggling with them while holding the spring in compression (the mainspring vise would avoid that for you!).
With the spring compressed just enough to take the upper arm pressure off of the hammer, remove the bridle entirely and lift the hammer off of the plate.
Now with the spring still held in compression, take your other hand and simply hold the sear in it's position by upward pressure on the tail (horizontal extension).
It takes very little to hold it against the spring as you have so much leverage.
Now release,,slowly,,the pliers/vise on the mainspring to allow the spring to relax. The upper leg will extend up and stop against the rear bridal bolster on the lock plate. It's almost all the way relaxed but still has some compression in it.
Now at this point you have in your hand,,held in place easily by one finger and your thumb, the partially compressed mainspring and the sear.
Lastly, grab the lockplate anywhere convenient and allow the sear to rotate under the partial spring pressure. The tail will rotate down and towards the front. As it does the spring is totally relaxed and the sear is simply lifted from the plate. The mainspring falls free of the plate.
To re-assemble.
Place the mainspring onto the plate with the longer leg up against the rear bridal lug and the 'V' up under the headless screw at the rear of the plate.
Place the sear in it's pivot hole with the tail well down and forward so it is not engaging the spring. Now rotate the sear backwards engaging the mainspring and taking it into partial compression.
At this point lay the plate on a flat surface,,grab ahold of the bottom of the sear and the top of the spring leg and compress with your pliers/vise enough to drop the hammer into it's pivot in the fired position.
The bridle then drops into position and screws down.
If you grab the spring too far forward, you won't be able to drop the bridle into place. Simply hold onto the sear and reposition your 'pliers' or vise and try again.
Of the two screws in the bridle,,the rounded head one goes in the rear position. The flat headed one is fitted in the front position to lay against the frame edge inside and level the plate surface on the exterior. You usually see file marks accross it,,the head filed flat but at an angle. Sometimes a witness mark also.
Doing any of this should not leave any marks, gouges or scars on the parts especially the spring. That can weaken it. Some of the springs are nicely finished,,others rather crude looking in comparison. But adding nicks and dents to them can only damage or weaken it.
DON'T use a side cutters to grab, hold and compress mainsprings like someone I know.
