First it looks like the flint protrudes out a bit to far.
I also agree about getting a different flint. Gun shops like to sell agates. they cost more and the mark up makes for more profit.
Your hammer doesn't look right for the rest of the gun. Are you sure that is the right hammer?
Hammers are supposed to be shaped so that the arc followed by the edge of the flint closely approximates the arc of the frizzen face, just enough off to nudge the frizzen open. Yours looks like it bashes high on the frizzen at an angle that isn't sharp enough. Looks like the lock geometry is off because of the hammer.
Can you post a picture showing more of the gun? OK saw the picture and thread. Markwell explains alot. Markwell was about as low quality as anyone would dare to sell in the US in the 1970's. I does look like the CVA Colonial pistol clones that many companies sold. But all is not lost. The weak point is indeed the lock. I don't believe that anything is bad about the rest of the gun. I do believe that on older CVA colonial pistol lock would fit your gun. Quality control was alot better on CVA stuff, but still not great.
The problem is that even the early CVA flint locks were'nt that great. From what I see, your lock plate shape is that your lock is probably nearly the same as the very early CVA flint locks. From about 1974 on CVA used a slightly larger and slightly better lock on it's products. Those won't fit, without a lot of inletting. Even Dixie Gun Works doesn't list a hammer for that lock.
You are probably stuck looking for another lock, or hand fitting a flint hammer from another gun. Such locks and guns come up on Guns America and Gun broker in various conditions almost weekly in percussion. (Compare the length of the lock plates, CVA used two different styles of percussion locks in their Colonial Pistol) In flint maybe a couple times a year.
An easy short cut to get an extra millimeter or two space for the flint, is to cut a round hole in the center of the flint leather and reinstall the flint into the jaws with the missing thickness of the leather where it abuts the jaw screw, you pick up some space. It could break the back side of the flint if the flint is pushed back too far and up against the screw.
If the gun was commercial, a larger picture would permnit us to compare it with known products.
To me the lock plate looks like a later 1830's civilian style lock with a mid 1700's style martial hammer. Granted a few guns continued to use that style hammer into the 1800's, (like the Harper's Ferry) but something just doesn't look right.
There were some odd mismatched style guns and locks sold over the years, Markwell was one of the offenders.
