The Quality Flintlock by Jim Chambers

[Blackpowder Barbie]

Here is a copy of the information we have about what makes a quality flintlock.  Perhaps Dad will elaborate on this soon.

THE QUALITY FLINTLOCK

There are features common to all flintlocks which must be present if the lock is to be reliable, consistent from shot to shot, and long lasting.

A.   Exterior Geometry

• 1.   Cock throw (the distance from the center of the square tumbler hole to the lower jaw) – this distance should be equal to or slightly longer than the distance from the center of the tumbler hole to the face edge of the closed frizzen.
• 2.   Angle of the Jaws – The line of the lower jaw should intersect the pan just forward of the pan center.
• 3.   Frizzen Spring Screw – Should be under frizzen pivot.  This has more to do with aesthetics than with function.
• 4.   Center of Tumbler – Should be on midline of the lockplate.
• 5.   Frizzen Spring – There should be minimal space between the upper and lower leafs.  The upper leaf should be almost straight, or it should have a slight hump bent into it.  Be sure to consider style and period.  Ideally, the frizzen should snap forward just as the flint reaches the bottom of the frizzen face or at about 30.  The frizzen spring should have power in balance with the mainspring.
• 6.   The cock should have a long arc of travel with half cock being located at more than Ύ of the arc.  The inertia built up during this long travel enables the flint to quickly and consistently scrape the frizzen face for a large shower of sparks.  A short arc of travel is fine on a percussion lock but undesirable on a flintlock.
• 7.   Pan Cover – The pan and pan cover should fit together tightly.  A raised lip around the pan, which is recessed into the frizzen, is historically correct on some English and Continental locks, and adds a degree of waterproofing.  A projection on the pan cover hanging down into the pan neither waterproofs nor is historically accurate.  This arrangement simply obscures light and prevents one from seeing how closely the pan and pan cover fit together.

B.   Interior Geometry

• 1.   Mainspring – First and foremost, the mainspring should have plenty of power.  Power in the spring equals speed, consistency, and an abundance of sparks for sure ignition.  There should be minimal space between the upper and lower leaf.  The lower leaf should have a fair amount of curve when at rest.  As the cock moves from rest to half and full cock the lower leaf should be straight.  The spring hook at rest should be at the tip of the tumbler foot and should move up very close to the tumbler’s large shaft when the lock is at half cock.  The tumbler should simply turn under the hook nose from half to full cock.
• 2.   Tumbler – The optimum curve of the tumbler foot is this:
  This specific shape maximizes the power of the mainspring from rest to half cock and reduces the cocking force from half to full cock. 
  There should be a .005” to .010” bearing surface around both axles to keep the tumbler body from rubbing the plate and bridle.  The cock notches should be concentric with the center of rotation so that the sear bar will be at the same position at rest, at half, and at full cock.
• 3.   Sear – The sear pivot screw is set close to the midline of the plate on early locks, lower on late period locks.  The sear nose should be smooth, square, and parallel to the tumbler notches.  A bearing surface around the pivot hole is desirable.
• 4.   Sear Spring – Should be fairly heavy and should bear near the sear pivot for a light, crisp pull.  Some curve in the lower leaf is desirable.
• 5.   Fly – The only function of the fly is to keep the sear nose from falling into the halfcock notch.  It is necessary in a lock only if set triggers are used.

C.   Fit and Precision – This is a must to prevent binding and wasted power, to increase speed and reliability, and for even, long wear and lock life.

• 1.   All bearing holes should be drilled undersize and then reamed to specific diameters.
• 2.   The frizzen pivot screw hole should be reamed to within .001” of the screw size and perpendicular to the plate and pan bridle.  This will prevent binding and assure a tight pan cover to pan fit.
• 3.   The sear pivot hole, likewise, should be reamed to within .001” of the screw size.  An oversized hole will result in a heavy trigger pull with much ‘creep’ as the trigger takes up the slack between the pivot hole and the screw.
• 4.   The tumbler axles must be lathe-turned for roundness, smoothness, and for a tight fit in the plate and bridle holes.  Both axles should be within .001” (+/- .0005”) of the respective holes.  A loose fit here (.004” or larger) will result in power robbing wobble as the hammer falls.  A rough, undersized, out of round shaft turning in a hole will accelerate wear.

D.   Polishing – Reduces friction of moving parts.

• 1.   The interior of the lockplate should be polished to a 400 to 600 grit.
• 2.   All moving parts (tumbler, sear, frizzen foot, frizzen spring, mainspring) should be polished to reduce friction, to increase speed and to improve consistency.

E.   Heat Treating – Most manufacturers now supply springs that are ready to use.  No further heat-treating is necessary.  The frizzen and internal parts should be hardened and tempered according to the manufacturer's directions.

F.   Conclusion – The function of a lock is to ignite the main powder charge.  Some locks do this very quickly and consistently.  Others do not.  Good locks have several things in common: good design and geometry, quality materials throughout, and precision assembly.  Most locks will ignite the charge most of the time, but only a precision lock will fire the gun reliably and consistently from shot to shot under all conditions.  A “quick” lock is certainly desirable, but, if accuracy is your goal, consistency from shot to shot means more than speed.  Precision equals consistency.  Consistency equals accuracy.

[TgeorgeZ]

Are there any BOOKS out there on locks, their history, different types, and tuning them?  They fascinate me - how they ever designed such a thing.

[derringermike]

great info,,,anything like this for percussion locks? I'm building a single shot percussion deringer from scratch...any help would be thanked   mike

[Artificer]

Miss Barbie,

Thank you very much for posting this.  Very informative.

I've got three additional questions.

How much distance should there be from the bottom of the sear and bridle screws to where they contact the bridle?  No more than two or three thousandths of an inch?  I realize you have to custom cut the screw thread to do this.

Second question, how much distance should there be between the bridle and the tumbler post and the bridle and the top of the sear?  I'm thinking two or three thousandths of an inch? 

Third question,  how do you tell when you have a good "tip over"point on the bottom of the fizzen where the frizzen spring engages it?   

Thanks for any further information.
Gus Fisher

[D. Taylor Sapergia]

Gus, your first two questions sound like clearance/contact questions.  The bridle screw(s) that hold the bridle to the plate should be tight.  The sear screw should also be tight, but should not pull the bridle down onto the sear, impairing it's travel.  Most commercial locks do not provide for this, so I just put the screw into the drill press chuck and with a file ground safe on the thin edge, I dress down the inside face of the screw, checking often so that when done, the screw bottoms in it's threaded hole in the plate, but the sear still is able to rotate freely.  It doesn't matter to me how many thou that is - I don't measure it.
The bridle keeps the tumbler and sear rotating in a flat plane, parallel to the lock plate.  So dress and polish the inside of the bridle so that while the bridle screw(s) hold the bridle tightly against the plate, the tumbler and sear can rotate freely.  Too much, and you may have detent issues...too little and the tumbler and/or sear will bind.

[northmn]

Great info.  Acouple of points for discussion:
I really have little problem #7 Exteriror As to the pan cover projection I feel you are positively correct, but they do help hold in the primer for carrying if the fit is not tight as possible, using 4f. If the fit is atrocious they do not do that.  I will state that I ahve an older Siler Chambers lock that has a very good fit.
Long throw:  Late English locks used a stirup, strong mainspring and shorter throws on the theory of increasing lock speeds.  They also may have used smaller flints.  Is the longer throw also a means of using a larger flint which in itself is more reliable? 
I had to balance two locks for frizzen spring mainspring balance.  It is a bit tedious, I would go so far as to call one a B---h.  In one case it was a matter of slowly lighteneing both springs as the lock would destroy a flint in a couple of shots.  In another I installed a "roller" in the frizzen to get enough tension so that it would spark.  Both worked.    I have bent a lot of hammers to get the things to perform correctly in the earlier build days with Italian and some American made locks.  Thank heavens for outfits like Chambers. 

DP