Remember. "Your mileage may vary".
There is a lot of misunderstanding about springs.
Strong springs don't eat flints. I too used to believe they did till about 4 years ago.
Strong springs make faster and more reliable locks.
But if the lock design does not favor strong springs there will be problems. So change it. Usually flat faced frizzens are the problem OR the frizzen is too heavy and this causes it to store too much energy or have too much inertia.
Mushy frizzen springs will break flints since they will allow the cock to excessively accelerate the frizzen (unless the mainspring is mushy too) then since the frizzen is moving too fast the mushy spring compresses and then throws the frizzen closed to either strike the top jaw or more likely the flint and break it. If the lock breaks flints in two this likely the cause. The frizzen spring does far more than hold the frizzen closed. This is why late locks, the good ones, have rollers and some form of ramp to INCREASE the pressure against the cock as it is scraping the frizzen face and
I usually INCREASE the tension of these two springs in every lock I get. Either by re-arching or making new ones. Often the temper of the spring is not right and it needs to be heated, bent to a better shape then quenched and tempered. In general the preload on most cast springs is far too light. Many good forged springs need to be compressed 1/2" or more to be put in the lock. But they are often 1/2 or less the thickness of the cast spring. Even castings of springs from old locks are wrong since often the original spring has relaxed over the years and is now much weaker than during its service life.
We also must remember that a great many original American rifles have low quality locks and/or are 20-40 years behind state of the art when the rifle was made.
The flintlock, at least is England went through a great number of changes from 1780 to the 1820s alone.
These are state of the art locks circa 1800.
Look at the relationship of the bottom jaw to the pan and the angle it would have when the flint strikes the frizzen.
Also note where the flint strikes the frizzen. This was likely one reason why frizzens got smaller in the later English locks.
The linked mainspring, *if done correctly*, gives light pressure at the sear on full cock and increasing pressure on the tumbler as the cock moves toward it resting place. A "plain" tumbler will do this to some extent as well if the spring and tumbler are properly designed and installed.
In other words on a GOOD lock with GOOD springs as the cock is drawn back to full cock the pressure required to draw it back is reduced. This was called the "heavy first lifting" by Forsythe when speaking of the percussion guns, but the internals on the British percussion gun of the 1840s-50s is identical to the internals of the late flintlocks of 1810-1820.
So all parts need to work together. A strong mainspring and a weak frizzen spring will allow the cock to fling the frizzen open with hardly any contact with the frizzen face and the frizzen will likely rebound and break the flint, sometimes almost EVERY SHOT. BTDT. Sometimes the frizzen will strike the top jaw of the cock making a dent.
A significantly stronger frizzen spring may cure this though the frizzen foot may need reworking as well and the frizzen face may need to be curved.
If the the frizzen spring is too strong and the mainspring weak the frizzen may stop the cock. So I would increase the preload on the mainspring or make a new one.
Then we have how the flint strikes the frizzen. If the flint strikes the frizzen face at a 90 degree angle then the flint may break, curving the frizzen face or bending the cock may well cure this by changing this angle. Locks won't spark if the frizzen is too hard, or at least not as well, nor will they work well if the frizzen is too soft. Too soft and result in no sparks or in the flint digging in to deep and thus breaking or chipping back faster.
Look at the relationship of the cock to frizzen here and the point where the frizzen pivots.
This lock, once the springs are STRENGTHENED works very well and hardly jars even a pistol.
Look at this lock
This lock was built from barstock and castings by a friend a long time ago, well back before 1980. It has a vary fast cock speed.
This lock was the most horrid flint eater I ever used, I lightened the M spring and all this did was reduce reliability with some saving in flints. I even put a little curve in the frizzen to no avail.
At Don's recommendation I replaced the frizzen with the smaller one from the L&R above, this allowed me to put a stiff spring back in it and cured the breakage problem.
Note this casting of a late Manton lock.
Note the distance between the center of the pan and the frizzen pivot. This changes the way the frizzen rotates as the cock pushes it open and it would seem increases efficiency. This lock give as good a life as most locks I have owned and the flint almost never needs knapping. If the lock stops sparking usually the flint is so far gone that knapping only gains a shot or two.
Even though it has a significant ramp on the spring it still comes back and strikes the top jaw sometimes and I likely need to change the ramp to see if this is preventable. I had to face the frizzen and this may have increased the weight of the frizzen enough to cause this (?)
Castings are often not identical. A cock casting, for example, from an identical lock from the same maker may be subtly different than another and this can cause problems that bending the cock, usually down, will solve.
I think the practice of using flints upside down may stem from cocks being too large for the lock or having the wrong bottom jaw angle. But this is almost a separate topic.
At any rate if the lock has strong springs rejoice. If it eats flints try to figure out why before attacking the springs with a belt sander. I have learned the hard way that this it not necessarily the right answer.
I had a L&R large round faced lock that would hardly spark. I shimmed the MS with a piece of brass between the legs and this helped a great deal. I then ordered another to see if this would cure it and lock was fast, sure fire and easy on flints, very, with the stronger spring. BUT. These locks use LARGER flints as well that are more durable.
Today I would rework the original spring. But this does not always work. I tuned a "Lott" lock from a trade gun a couple of months ago and when rehardened and tempered it broke at a flaw near the bend that in its weak state was not a problem. So I forged a spring for it. But the tuning bill was 120 bucks by the time it was working right, since it had other problems as well.
Of course one cannot use a 1820s Manton lock on a 1750s rifle or fowler. BUT one can look at the angles and such and the radius of the frizzen face and make improvements that do not change the locks suitability for the given time period.
This is a cheap lock probably of the 1820s-50s. But note the radius of the frizzen face. Also note the cock stops far from where it should as well.
So if the lock is reproduced as is for a "trade gun lock" is will be "right" but its also "wrong" for good function.
As is this P.O.S. lock from an 1840 Connestoga Rifle Works rifle that as near as I could tell had never been fired much less converted. Considering the cock position it might not work at any rate. Yes its down not at 1/2 cock.
It looks like something "Dilbert" would receive from "Elbonia" if he were having flintlock parts made.
When we look at old rifles and the locks they have installed we much remember that they.
#1 Have likely been reconverted to flint so the lock is NOT as it was in 1775 or when ever.
#2 That the parts were likely what ever was available and the person ordering the work done or doing it cared little of the lock was functional so long as it looked "OK" when on display.
So we have locks on rifles that were never there if the lock is replaced, perhaps much like the Leman marked POS pictured above.
Or we have locks with a refitted cock and/or frizzen and spring that are the WRONG SIZE and/or GEOMETRY to work properly with each other. So if someone gleefully reproduces this in making a rifle they find that they have to jump through hoops that they should not have to in order to make the rifle work. Its "right" for how the original rifle looks *now* but that does not mean this is how the rifle looked, or functioned, when new.
Then also think "copied age flattened springs " and many things become less murky.
Nor can I say that some, a few or many old locks did not break flints.
Dan
