And make sure its not simply coming back after being full open.
Unless it stops the cock and fails to open this is often the case. Slow motion testing by letting the cock down with your thumb will tell if it kicks open as the flint comes off the bottom of the frizzen. Even then inertia may carry it open anyway.
Stopping the cock us usually a weak mainspring or a too soft frizzen and the flint digs in.
In my experience, weakening springs is a bandaid for some other problem which the process may not fix as desired.
This is a very reliable lock. Easy on flints, think I got 150 shots at LEAST from the flint shown. Large Siler frizzens with no change in the toe shape. I find that the Siler frizzen with the toe canted back, TOW sells them, opens too soon but I have not tried it in a standard lock.
But its not the fastest. Needs more mainspring but this would require a major remake of the internals.
HOWEVER. It works far better with one English flint than with another. The flint is a major variable in flintlock performance. Its not all the same unless you get a batch of flints all made from the same core and maybe not then.
This could be another factor in the bevel up/bevel down thing as well (??)
This lock is fast and reliable gives reasonable flint life and has springs that would make the advocates of light springs have thumb cramps cocking it. But flint life takes second money to going off when desired. It seldom needs to have the flint knapped and actually once the flint stops working it can't really be sharpened and used more than 1-2 shots with out more misfires.
I lightened to springs on my Don King flint Hawken to the point it nearly quit sparking. Don then told me to put on a L&R #1700 frizzen which fits perfectly with a little fitting. I then got a new mainspring, from the guy that bought all Don's stuff when he moved to Billings, and its really strong, but the lock no longer breaks flints since the new frizzen has a curved face, the old one was too flat even after I put some curve in it. I don't know what it was cast from but it did not want to bend.
This rifle would break some flints on the first shot. And honestly this may have been *frizzen rebound* as this can be a factor and can break the flint off even with the lower jaw at times.
One other thing a lock may work differently in the gun than out. Either because of possible wood binding slowing movement OR because being fixed in the gun makes the parts work right. No movement of the plate when installed in the stock as is possible when hand held.
Dan