Can a mainspring be made stronger?

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ThumperJones

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I've got a Fusil De Chasse made back in the 90s. It shoots alright and is mostly reliable as long as the flint is "just right" and everything is just how it needs to be. I believe that the mainspring is fairly weak, as it takes considerably less force to cock than other flintlock I have messed with. I don't have a way to measure it, so i apologize in advance for those who need numbers on these kinds of things.

The lock in question is an L&R Trade Lock. Very low round count, around 100-150 at most. I have disassembled it and made sure everything was smooth and lubed. I have been told by a few people who I consider wise on the subject, that these locks are fairly notorious for weak mainsprings. The lock is also suspiciously easy on flints. It always sparks, but nothing like my others and seems noticeably slower.

Is there anything I can do to the mainspring to give it a little more oomph? Maybe heating it and opening it up a little more? I was planning to contact L&R to order a replacement, so figured I had nothing to lose. I have an assortment of torches and metal working tools. Just looking for some tips. I appreciate your thoughts!
 

Zonie

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IMO, heating and trying to bend the spring is the worst thing you could do. The chances of you being able to re-heat threat it to over 1500 degrees F, quenching it and then tempering it correctly are slim.

You can try to put a thin wedge of material in the area of the bend where the spring doubles back on itself to form the lower leaf but this is risky.
If the wedge is too large, the spring will be over-stressed and it will break.

If it is making enough sparks to fire the gun I strongly suggest you don't mess with it.
Work on finding really good flints that make a lot of sparks and be happy.
 

FlinterNick

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to make a spring stronger, you'd want to reharden and temper.

Bending the end of the spring slightly is a method recommended by Kit Ravenshear (refer to his books) however it is only temporary as the bend will wear back.

, get a new spring in cast form 6150 steel is your best bet

Or

You could get a Ford break leaf spring and cut the spring out of it, shape to the lock. This is of course very crude but will produce the strongest spring. I've done this on some guns, it takes time with success and failure.
 

Zonie

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IMO, just re-hardening and tempering a spring will not change the force the spring can produce.

The strength of a leaf spring is dependent on the thickness and width of the spring and to a lesser degree, the material the spring is made from. It is also a function of the amount of deflection the spring is bent when it is under load.
Just re-heat treating a spring will not increase the springs power unless the spring is reshaped while it is in the soft, annealed condition to cause the spring to be bent further. Doing this requires the spring to be annealed, reformed, hardened and then tempered. That hardening and tempering part is what I mentioned above when I said doing this can cause problems.
 

ThumperJones

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Thanks for the advice guys. I'm going to call L&R shortly and see if I can buy a spring. If so, I may try the whole annealing and reshaping deal. Nothing to lose, and I may learn something I can use later.

But I ain't gonna try it just yet, there are squirrels to hunt!

Thanks again fellas
 

Rat

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I would try the wedge-thing, as mentioned by Z, first. This worked very well on my Brown Bess main spring, which seemed weak. On that lock, the spring is nice and long, which I believe lessens the chance of it breaking. You don't have to increase tension very much, to get better results.

What is used for the wedge will also decrease the chance of breaking. (which I think is a small chance) Brass or steel, maybe not. Lead or leather, probably best. I think I have a wedge of leather in mine, and yes over time probably needs to be replaced periodically, although mine is still going fine after years of being in there.

Good luck!

Edit: oh yeah, wedge should have tapered ends, no sharp corners resting against the spring.
 

ThumperJones

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I called L&R and ordered a new spring. They said my lock is old enough to have a cast spring, and the new ones are forged. The new spring requires a new hole to be drilled, but nothing major. Should be a major improvement. Seemed like great folks to deal with.
 

rich pierce

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Great to hear.

For the sake of discussion an old period wilderness fix was to pound a smaller v spring into the bend of the mainspring. Booster spring. I think they called it a turbo booster. Just kidding but many old locks have been found like this.
 

FlinterNick

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IMO, just re-hardening and tempering a spring will not change the force the spring can produce.

The strength of a leaf spring is dependent on the thickness and width of the spring and to a lesser degree, the material the spring is made from. It is also a function of the amount of deflection the spring is bent when it is under load.
Just re-heat treating a spring will not increase the springs power unless the spring is reshaped while it is in the soft, annealed condition to cause the spring to be bent further. Doing this requires the spring to be annealed, reformed, hardened and then tempered. That hardening and tempering part is what I mentioned above when I said doing this can cause problems.
For a spring that is already made of low quality steel and is too light for the lock, I agree hardening and temper again will not provide much benefit.

For a quality spring that was not hardened and drawn correctly, this could be done to remedy the issue.

If the spring is made of poor quality steel, it just wont matter how much you temper it.

I replace my pedersoli springs with 6150 cast springs as soon as I purchased them. The pedersoli springs are often undersized.
 

Rat

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Great to hear.

For the sake of discussion an old period wilderness fix was to pound a smaller v spring into the bend of the mainspring. Booster spring. I think they called it a turbo booster. Just kidding but many old locks have been found like this.
That actually sounds like an excellent idea, would not stress the larger spring, and might actually result in superior "spring action". I believe that leaf springs on a car/truck have some advantages over coil springs, (or a single spring) kind of the same principal. (of course, most cars/trucks now have coil springs, as they are much cheaper to make) (non ML content!)
 

FlinterNick

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For the French and Indian war I’d look no further than and track of wolf Brown Bess marked Wilets.

then on the French side militia house in Ohio makes a nice 1730 Era French banded musket.

The problem with trade guns like a de chase is that you’re basically opting for irregular militia while militia could use both military and trade.
 

dave_person

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Hi,
As Zonie wrote, hardening and tempering won't improve strength unless the original spring was tempered too far and is weak because it took a set. Then hardening and tempering at the proper temperature would resolve the problem. A new forged mainspring by L&R should solve your problem, however, they are mediocre springs. If you are getting a replacement, there is no reason not to mess with your current spring. You can improve and increase the strength by first annealing the spring. Then heat the main bend red hot with a MAPP gas torch and hammer it tighter or even closed. After that, heat the lower leaf of the spring and when red hot, use pliers to pull the leak downward from the hook to create a gentle arc. That is called "pre-load". After bending check to see that it will engage the tumbler properly and is bent downward enough to keep strong pressure on the tumbler. Don't go over board on the bend, just enough so that it must be compressed a bit to put it in place when the cock is at rest. Next, heat the spring red hot again and let cool to normalize it and eliminate internal stresses caused by the hammering and bending. Heat again to red hot, quench in oil (I use canola oil) and clean off the oil. If you have a lead pot, turn it up to 700 degrees, let the spring temper in the molten lead for 1 hour, remove, and let cool. I do this with a programmable heat treating oven but a lead bath works pretty well. If you don't have a lead bath, polish the hardened spring bright. The heat it evenly and slowly with a propane torch. The bright steel will change colors as it heats up. It will go from pale yellow, to purple, to bright indigo blue. At that stage go very slow and watch it change color until it turns a light sky blue. Stop heating and let cool. It isn't a bad idea to polish the spring again and temper to sky blue again. Then try to spring. Compress it slowly and in stages in a mainspring vise, then fit it in the lock and try it. If it breaks, well you have a replacement coming. If not, you may end up with a better spring than the replacement. The bottom lock in the photo below shows an L&R lock with new forged mainspring. The upper lock is a Chambers round-faced English lock and the middle lock is from an original English fowler dated to the 1760s. Note the L&R spring has no shaping or tapering and is crude by comparison.

The photo below shows a proper mainspring. Note the tight main bend and the arc (pre load) in the lower leaf.

This photo shows a different lock with the cock at full. Note the lower leaf of the spring is straight and there is no bend upward in the middle. That means the whole leaf is working and not just the middle of the lower leaf.

dave
 

ThumperJones

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Dave, I very much appreciate your post. That's some great information that I'm glad to have! Soon as the new spring shows up and I make sure it will fit, I'll see what I can do with the original. I'm excited to play with it.

I don't have a lead pot, but I have propane and oxy/acetylene torches. I'll have to go by feel and your excellent instructions.

I'll probably take the gun hunting in the morning. I'm sure now the spring will break just since I've been talking bad about it! :)

Thanks again, I owe you one bud!
 

Rat

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Lead pot? Does the wife have a cast iron fry pan she won't miss? They make great lead pots. :) Seriously.
 

dave_person

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Hi TJ,
You are welcome. Did you look at the photo showing the lock with L&R spring? Note how the upper leaf butts into the bolster on the lock with no tab or extension. That may be different than your current spring and require you to inlet the new one. It is also possible the upper leaf will not clear your barrel or fir in the current inlet.

dave
 

M. De Land

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I've got a Fusil De Chasse made back in the 90s. It shoots alright and is mostly reliable as long as the flint is "just right" and everything is just how it needs to be. I believe that the mainspring is fairly weak, as it takes considerably less force to cock than other flintlock I have messed with. I don't have a way to measure it, so i apologize in advance for those who need numbers on these kinds of things.

The lock in question is an L&R Trade Lock. Very low round count, around 100-150 at most. I have disassembled it and made sure everything was smooth and lubed. I have been told by a few people who I consider wise on the subject, that these locks are fairly notorious for weak mainsprings. The lock is also suspiciously easy on flints. It always sparks, but nothing like my others and seems noticeably slower.

Is there anything I can do to the mainspring to give it a little more oomph? Maybe heating it and opening it up a little more? I was planning to contact L&R to order a replacement, so figured I had nothing to lose. I have an assortment of torches and metal working tools. Just looking for some tips. I appreciate your thoughts!
I used to follow the elaborate protocol for spring tempering as is found in various publications on the subject but most of them are based on per inch of thickness of the steel in question and a new main spring will have many times less mass. I read in one of my gunsmith books about an old black smith trick of mixing a 50/50 solution of 30 wt oil and Kerosene, covering the spring in the solution on it's side in a small flat dish and lighting it with a propane torch. Do this out side and let it burn it self out. It will take 15-20 minutes but the spring will be as well tempered as any of the sophisticated protocols produce. I have used it for many years and have never had it fail. Simple easy and effective!
 

dave_person

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Hi,
I used to use that method and half the springs were mushy. For me, there is nothing easier than popping the spring in my heat treating oven for an hour, and there is no smoke.

dave
 

bud in pa

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How about a toaster oven and an oven thermometer, I read that in a knife making book.
 
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