It's a lock out of a CVA colonial pistol kit from the 70's.
Pushing down on the lock causes the arm to flatten out and be closer to the base, but then the trigger release goes from a 10-gorilla pull to a 25-gorilla and an elephant pull, and after the first hammer release, the spring moves back out like the photo shows.
Actually, the mainspring has little to do with the amount of pressure it takes to "trip" the sear bar.
I do have a main spring vise and I've removed the spring in the process of taking the whole lock apart for cleaning. Putting it back together is when I noticed the difference of the spring arm. However, I'm thinking it was like this all along, I just didn't notice it and now as I'm putting the kit together, I'm thinking of taking care of the issue, if there is one, as well as trying to lighten up the trigger pull.
Sounds like maybe you didn't get the lock put back together quite right. (that is the first thing I would check)
Going back to the kit, I'm not 100% sure that someone didn't try to put this thing together before I got to it. It seems that parts of the kit were put together already. It wasn't me that I'm sure of, but I do not recall where I got it (garage sale?)
There is also the chance that the previous owner had it apart,... and didn't get it back together right.
If your kit is a CVA,.... then your lock is a spanish-made "Maslin lock",.... replacement locks are available from Deer Creek, and you might also be able to get one from "Traditions", and "Track of The Wolf" also carries them
part # Lock-LR-01-F for flintlock, and
part # Lock-LR-01-C for percussion,... if worse comes to worse.
Personally,... I've
never seen a mainspring sit as cock-eyed as that one, and that is why I suspect there is something wrong with the way it was put back in the lock.
The problem of heating the mainspring up enough to bend it, is it will cost you the "temper" in the spring,... unless you are familiar with re-tempering springs.
I wish it was in my hands so I could look it over more closely.