TUNING THE FLINT LOCK

Wayne Anderson

GEOMETRY

When flintlock geometry is referred to, it's usually one of two areas, cock to pan or frizzen snap over.

The Cock Area When the cock is in the down position the shoulder of the cock should rest on the lock plate and the tumbler should have slight clearance from the bridle. The bridle is the backup stop in case the cock or tumbler arbor fails. The bridle must stop the tumbler rotation before the mainspring comes off the tumbler hook. The tip of the main spring should be well supported by the tumbler hook in the down position . The cam/hook of the tumbler is designed so that it will transfer the pressure of the main spring with maximum force at the end of its travel. With the hammer down the mainspring acts near the end of the cam with greatest leverage. As the hammer is pulled back the tip of the mainspring moves along the cam toward the axis of the tumbler, decreasing the leverage. The stirrups in later locks reduced friction by changing from sliding friction to rolling friction. If the main spring is not retained on the hook it can splinter the wood in the bottom of the lock mortise area if the cock arbor fractures. Locks with stirrups also have this hook to catch the main spring if the stirrup breaks during cocking.

The flat surface of the pan and the bottom jaw of the cock are your main reference lines for lock geometry. At half cock, the jaw of the cock is parallel to the pan. In the down position a line extended from the bottom jaw points into the center of the pan, making approximately a 40-degree angle with it. The cock must fit very snugly on the tumbler arbor, with no play or free movement. The cock should not touch the lock plate any time during its movement until the shoulder contacts the plate. The jaws of the cock should be long enough to securely grip the flint. The cock screw is set well back in the cock and the screw top must not contact the frizzen during its movement.

The top jaw has the top slanted to the back and down slightly so that the jaw has a more effective grip at its outer edge. The throw of your lock (flint) is the distance from the center of the tumbler arbor, perpendicular to the bottom jaw.



Frizzen Area The frizzen must cover the pan in the closed position so that no light shows through when viewed from the touch hole side. The tail of the frizzen should only contact the frizzen spring, not the lock plate. The nose of the frizzen should hold the frizzen in contact with the flint until the flint just passes its bottom edge then it should snap the frizzen into its full open position so that it does not block the path of any spark into the pan. Frizzen spring tension is a balance of the frizzen spring and the main spring force. The main spring must be able to scrape the flint across the frizzen with small loss of speed while the frizzen spring maintains firm contact between the flint and frizzen. The flint produces sparks by scraping off white hot particles of metal from the frizzen. On a correctly hardened frizzen these will be abundant and white hot. On a soft frizzen there is not enough friction during this cutting action and particle do not become hot enough. On a frizzen that is too hard particles cannot be scraped off. A correctly hardened frizzen will usually test in the 55+ range on the Rockwell scale. This is about the same hardness as a quality knife blade.

(For further frizzen hardening information see the "Tempering Steel" FAQ)

FRICTION-POLISHING

Friction is the major enemy in every lock. Lock filers went to great lengths to reduce friction wherever possible. The stirrup main spring reduced friction by changing sliding friction to rolling friction. Roller were placed on the frizzen spring, again changing sliding friction to rolling friction, slight shoulders were added to the tumbler and other parts creating "Frictionless" locks. Any place on your lock where metal touches metal should be polished and lubricated. The lock plate itself should be perfectly flat inside. The tumbler should be held by the lock plate and bridle so that it rides on only those two points (lock plate arbor and bridle) or as close to that state as you can get it. If either the plate tumbler hole or bridle hole is oversize this may be impossible without parts modification or replacement. You can polish anything you choose for appearance. Polished surfaces are more resistant to rust. Caution: over polishing can reduce the size and strength of parts.

FLINTS

Knapped flints are preferred to cut agate. Bevel up or down doesn't seem to matter, use whichever gives the best spark in your lock. Bevel down can give a longer scraping pass on the frizzen surface of some locks. The flint's initial strike should not be at 90 degrees to the frizzen face, but at a slightly greater angle, a scraping action is desired, 90 degree angle will just shorten flint life. The flint needs to be held very firmly in the cocks jaws. Two materials are used for this, leather and lead. Leather is the most common choice. Lead was used mainly in large military locks. Leather has the advantage of holding the flint firmly yet providing a slight cushioning to the initial contact, which can extend the life of flints. It is the scraping action that causes most of the sparks. To hold the flint firmly, it needs to be placed as deeply into the cocks jaws as possible. This distance can be increased by notching the leather or lead for the jaw screw. However, flint contact with the screw can cause notching on the rear of your flint. It is not traditional but it improves the rigidity of the flint if it is glued to the leather. The glue must be water and solvent resistant. The best I've found for this use is the gel type superglue's. Cock screws that are drilled are easier to tighten without damaging the screw. The slot was probably used more frequently in early locks. The slot on cock screws is not tapered like our modern screwdrivers. Using a modern screwdriver will distort this slot. Use a flat piece of metal or file a screwdriver to fit your cock slot.

Keep the flint sharp and clean. Cleanliness is an important part of reliable ignition. Make wiping the flint and frizzen clean part of your reloading practice. Watch for "Shiners" when you wipe powder residue off. Knap any shiners as they appear! Shiner is the term for the dull area that develop on your flint from use. They usually have a shiney metalic color to them, therefore the term - Shiners.

There is a real simple way to re-knap your flint faces. But it does require that you make a small tool. Take a large nail (about 3" to 3 1/2" common nail) and grind or cut the point off square. Then at the side of the now square tip take a file and cut a ledge about 1/8" back from the tip and about 1/2 way through the nail so that you create a "step" at the tip and on the side of it.

Next file on the side of the nail below the step so that the "front" of the step is flat and not the nail's rounded surface. (but don't go too far, leave at least 1/16" of step) Harden with a propane torch and quick water quench.

Take the nail to your flint while the flint is still in the jaws of your hammer. Cock the hammer. Put the step on the front edge of the flint, angle the nail forward towards the frizzen about 30 degrees off vertical (with respect to the flint) Tap the nail head with a small hammer just a light tap, not hard. A small piece of flint should flake off, and if you continue across the front of your flint it will re-sharpen the edge.

PANS, POWDERS AND PRICKS

Priming the pan - The pan should never be filled to the point where powder covers the touch hole. If the touch hole is covered, powder will have to burn down until it uncovers the touch hole before the main charge can ignite. The key is to be sure that the touch hole is clear so that the hot gas flash can get through the touch hole to the main charge. A technique used is to carefully place the charge away from the hole and not fill the pan completely(1/3 to 1/2), then to tap the rifle on the lock side just before firing to jar the powder away from the touch hole. Several late flintlock period manufactures even sloped the cavity in the pan slightly away from the touch hole. For quicker ignition use the least amount of powder that will ignite your main charge. Experiment to determine this amount.

Powder used in priming should be 4 F or finer. Fine powder ignites easier/quicker.

Vent Pricks serve two very important purposes. One is to clear the vent of debris, the second is to open a channel for the hot gas flash to the main charge. For reliable ignition it is common practice to insert the vent prick just before priming the pan and closing the frizzen. Some also force a small amount of priming powder into the vent with the prick, being sure to insert the prick at the finish, far enough so that the open channel is maintained. Since fine powder ignites easier, this small amount can't hurt and actually helps ignite the main charge. You are not trying to create a powder train. You are trying to place a few grains of fine powder into the surface of the channel that you created in the powder with the prick. You are not reducing, blocking or changing the channel in any way. Try it both ways and use what works for you, the important point here is to keep that flash channel open! Vent pricks made of bronze welding rod are recommended because bronze won't wear the metal in the touch hole like a steel prick will. Pricks that have 4 sides work well as the sharp edges help clear the fouling in the touch hole.

TOUCH HOLES

Size Touch holes generally fall in the 1/16 (.0625) to 5/64 (.078) inch range. Some preferring slightly large for smooth bore. The maximum is considered to be 1/10 (0.1)

Location A straight line across the flats of the pan should split the center of the touch hole. Or if not spilt by this line be just slightly below it. A hole placed too low will tend to get covered with powder causing erratic/slow ignition, too high can also cause erratic ignition by blocking some of the heat flash. A touch hole that is too high will sometime work best with a full pan of powder, often a poorly placed touch hole will need to be replaced by a touch hole liner.

Touch Hole Liners One of the problems with a drilled flash hole is that it results in a relatively long small passage from the pan to the powder charge. Touch hole liners are used for several reasons:

a.) To replace enlarged worn touch holes. Wear and corrosion are the main enemies of your touch hole. Liners are made of hard corrosion resistant materials.

b.) To get the main charge closer to the priming gas heat flash. Touch hole liners can be drilled concave on the inside to allow the main powder charge to get closer to the outside of the barrel and create a shorter path for the hot gas to travel.

c.) To correct poor hole placement.

d.) To be used as an aid in cleaning.

e.) Liners allow removal so that a small amount of powder can be put behind the ball, when a ball is loaded without powder by mistake.

FRIZZENS

The sear and frizzen should work freely when their respective pivot screws are turned in as far as possible. Screw threads should not extend into the pivot area. Polish the pivot area on screws. The frizzen face should be smooth but not polished. A rough face will quickly dull flints. The frizzen should test at a Rockwell Hardness of around 56. A clean frizzen surface sparks best, wipe it often.

SPRINGS

Springs are the heart of your lock. Polish all contact points. (Examples - main spring tip, tumbler hook surface, top surface of frizzen spring.) Make sure that the nose of the mainspring has clearance in the tumbler at the fully cocked position. Polish the springs themselves, a polished spring is less apt to fracture. Any scratches or flaws are potential fracture points. Caution: polish only, do not reduce the strength of the spring. Make sure that the spring does not bind anywhere during its movement. There should be approximately a 1/3 to 2/3 balance between the main spring and frizzen spring (by feel or trigger pull gauge).

WET WEATHER

a.) Use Vaseline to seal the edges of the frizzen and the frizzen-to-barrel line. The vee where the barrel and stock or lock plate meet can channel water directly into the pan. Fill this vee for about 10 to 18 inches in front of the pan. Use wax sparingly as over waxing can hinder lock speed, especially in cold weather.

b.) Change priming powder frequently.

c.) Use a Cow's Knee cover during wet weather.

d.) Carry in a manner to protect the lock from the weather.

Special Thanks to Craig Baker and Kevin Richard-Morrow for their help in preparing this FAQ.

Bibliography

Recreating the American Longrifle
Wm. Buchele & G. Shumway 1976

The Complete Rehabilitation of the Flintlock Rifle
T. B. Tryon Reprint 1972

1997 Wayne Anderson


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