A Percussion Mainspring Question

[bluenoser]

Howdy,
I am restoring a percussion shotgun and am in need of a little guidance.  The gun is a single and was made in 1853 by the Wm. Powell Co.  I had to make a new mainspring and had nothing but a bit of a shadow on the back side of the lock plate to go by.  It works OK, but the draw weight on cocking feels a little heavy and I want to avoid over stressing the stirrup and cross pin.  I will weigh it and am reluctant to weaken the spring without knowing what would be a good half cock to full cock draw weight to shoot for.  I intend to take measurements at the base of the thumb piece.  What would folks recommend?
Thanks for your help.

[JTR]

Interesting question.
From the base of the thumb piece;
On an original Nicolas Hawk percussion rifle I have, it takes 8 pounds to start moving the hammer back from half cock.
On a new Bob Roller flintlock I have, it takes 11 pounds to start moving the hammer from half cock.

I could imagine, when new, the Hawk rifle might have been a bit stronger, and after some time of use, the Roller lock might be a bit less.

John

[smylee grouch]

Yes an interesting question. I have an original H. Holland 13 bore side by side percussion that feels like it has stronger springs than any of the modern made locks I currently own. I'm thinking that the length of the hammer might have an effect on the poundage because of the leverage factor. 

[bluenoser]

It is a bit of a poser and both JTR and Smylee Bring up good points
If I am not mistaken, the mainspring in a flinter might be a little more stout than that of a percussion and I believe the length of the hammer probably would have an effect on draw weight.  However, I am hoping it might be safe to overlook those variables.  I measured the half cock to full cock draw weight on the percussions I have with the following results.  The full down to half cock draw weight on each was a little higher.
JTR's N. Hawk    8.0 lbs
E. Bond fowler   9.8 lbs.
Manton fowler    9.4 lbs
Nock fowler      11.4 lbs (converted flinter)
Bland fowler      16.75 lbs (this is a long barrelled 11 ga)
J. Harper double  R 12.25 lbs and L 13.6 lbs for an average of 12.9 lbs
If we drop the Bland as an outlier, the average is 10.3 lbs
The draw weight on the Wm. Powell is 12.6 lbs, so it might be a tad high.  If so, easily rectified by thinning the lower arm.
What would others recommend?

[Bob Roller]

Thin the lower limb and maybe make it narrower or polish it bright and heat the bend to a dark blue and let it cool.
Bob Roller

[bluenoser]

Thanks for your input Bob,
The steel is 1095 and I have a small digitally controlled oven.  The spring was heated to 1550 F, held there for 15 minutes and quenched straight in to canola oil that had been pre heated to 110 F.  It was then heated to 700 F, held there for 2 hours, step cooled and the whole tempering process repeated once.  I don't currently have access to a hardness tester, but expect it to be about RC 49.  It is polished bright and I believe the taper is appropriate but, yes, a little more taper on the lower limb would weaken it.  Thanks for bringing that to my attention.  Although I could be mistaken, I believe excess thickness in the lower limb is the more likely cause if the spring is too stiff.  As with tapering, that should be a simple fix.  The problem is that I don't really know what half to full cock draw weight I should be shooting for.
What draw weight did you shoot for when assembling locks?

[Bob Roller]

I saw and see no  reason to worry about "weight" as pertaining to cocking a lock of any kind so I can't give an answer to that question.
If it's a percussion lock the pressure needed to make the cap work and hold the hammer down on igniting the powder.Excess wear on the sear and full cock position will occur  with a strong spring and a lot of shooting.
Bob Roller

[bluenoser]

Thanks for the explanation Bob and I understand what you are saying.  This 175 year old lock has had a lot of use and abuse and has stood up well.  Hard to say what happened to the mainspring.  It will likely see a lot more use.  My main concern about an overly heavy mainspring was undue stress on the stirup and retaining pin.  I had not considered excess wear on the sear and full cock notch.  I do believe it is heavier than necessary, so think I will thin the lower limb a tad and test as I go.
Thanks for your advice - much appreciated