heavy mainspring

[RichG]

looking at my sons 50 cal Tenn. with a Siler mtn. lock. The mainspring is so heavy that after 12-15 shots a Michaels hot shot nipple will be so mushroomed that it's hard to put a cap on it. I have a wet sharpener and was thinking about grinding the spring thinner. Any pitfalls other than grinding to thin? Other ideas?

[Top Jaw]

I ground a odd ball replacement main spring  to fit an out of production lock once - using just a bench grinder and a small tub of cool water below it. Holding it in my fingers as I went, and dunking it after every few seconds to avoid over heating.  The long bottom leg is the one to focus on.   It’s also a lot of grind a little and try it as you go to find the right stopping point.  In my case, I also removed a little of the spring width near the bend to make this one work.  Your wet wheel should work.  Might still need to dunk it also, as you go.

[Marcruger]

I’d call Jim Chambers and ask his advice. He may have a suggestion. If nothing else, you get to talk to a really nice guy.  🙂 God bless, Marc

[Birddog6]

That's the trouble with those new fangled contraptions they come up with.   Caps ?     Never catch on. 

Call Jim Chambers & ask for Jim to call you back if he is not avail.  Always start at the Source & work
your way up to a resolution.  He built the lock, start with him.

If you are going to mess with the Mainspring, just buy another spring so you have a backup. This way if you
screw it up,  you can still shoot the rifle with the other mainspring. 

[P.W.Berkuta]

"If you are going to mess with the Mainspring, just buy another spring so you have a backup. This way if you
screw it up, you can still shoot the rifle with the other mainspring. " --- this is sound advice. I do this when I'm not sure my solution will work as expected - cheap insurance.

[Dphariss]

The percussion system is supposed to hold the cap on the nipple as much as possible. The better quality locks used the same internals as the late English FLs did and it caused what Forsythe calls “the heavy first lifting”. In flintlocks its increased the pressure on the cock as it scrapes the frizzen face. It would also reduce pressure on the sear at full cock. I believe that the “hot shot” nipple was intended to keep floppy coil spring locks from 1/2 or full cocking when fired. That they tend to spread gas and fragments is just icing on the cake.
In reading Forsythe’s “The Sporting Rifle and Its Projectiles” we find comments on weak mainsprings and potential lock damage in percussion rifles.
Since I cannot examine the lock in this case I have no idea if it’s REALLY that heavy or just too heavy for the nipple being used.  The soft alloy in the cap is supposed to somewhat protect the nipple. But if the nipple is made of 303 Stainless (it machines nice and is easier on tooling than most) or similar its not very hard and cannot be hardened or tempered. Not having seem the lock my first inclination is to put on a steel nipple and try that.

[Scota4570]

Having a heavy mainspring is desirable to keep the hammer from blowing back. 

Is the lock made with a flint style tumbler?  That is a very long hammer fall.  IF so the energy of the hammer strike will be large.  Would it be possible to move the full cock notch to shorten the hammer fall?  That would decrease the energy and maintain the the heavy pressure on the nipple with the hammer at rest. 

I'd try a regular nipple first though.

[Bob Roller]

I think this is another example of a stiff spring.Polish it as bright as possible and use a Presto lite propane torch and holding the spring by the stud then start a blue color at the end of the spring that hooks under the bolster and walk it down to the bend and hold it there for about 15 seconds and then continue on to the end of the spring.I have used this method for years on my forged springs and so far no reported problems.
Bob Roller

[Craig Wilcox]

Thanks, Bob - I was hoping someone would cover the heating method of easing a bit of tension on leaf springs.

I got a Traditions flintlock the other day.  The mainspring is fine, nice pull.  but the frizzen spring!  Dadgum thing is half an inch wide, and barely opens when struck by the flint, coming to rest just above the flint edge.  I plan to heat the working leaf as Bob suggests, AND to slender the thing down to about 3/8".  Will try one fix at a time tho, may not be a need for both "fixes".

[ScottH]

at the very least consider upgrading the nipple to one that is tougher, like these .....

https://www.buffaloarms.com/1-4x28-treso-ampco-t-c-nipple-tre115001.html

[RichG]

we've been using the hot shot nipple because they're what's available. Maybe I'll try an Ampco and see how it works before trying more involved methods.

[kutter]

You should be able to thin down the spring by using a file.
A clean sharp file will cut a tempered spring just fine. You have a lot more control in doing that as opposed to
going at it on a grinding wheel or belt grinder.
You have no fear of over heating using a file and little chance of taking off too much or simply mis-shaping it in a blinding shower of sparks.

Don't worry about directional file marks as you trim, thin and taper the arms down, though using a draw file technique is useful in doing this.

Get it nicely tapered to where you want it and then do the final clean-up to remove the file and  polish marks. Ending up with polishing lines going lengthwise on the spring to avoid stress points when it flexes.

[RichG]

Well I got brave and took a propane torch to spring. Easy watching the blue travel the down spring. Seems to have lightened the spring a little. I put a new hot shot nipple on and popped 24 caps and the caps still slide right on. Also ordered a couple Ampco nipple just in case.

Also, if the spring is still a little to strong, will it weaken the spring to much to polish and heat it again?

[rich pierce]

Weakening a spring by heating is not an approach I’ve heard of before. It could take a set or become completely un-springy if tempered too far.

[P.W.Berkuta]

Heat control with a torch is tricky -- I would use a lead bath with a thermometer. Start at a low temp - try - increase the temp - try again and so forth until you get the action you are looking for. Not knowing what steel the spring is made of is the problem when heating it to get it to relax some. It will be by trial and error I'm afraid. You may want to find a heat-treating chart that has different spring steels listed to guide you on tempering temps.

[Bob Roller]

Weakening a spring by heating is not an approach I’ve heard of before. It could take a set or become completely un-springy if tempered too far.

I have used this on a few springs with no problem and it's all I have ever used in all my new locks and they are all over the world and so far no reported problems.I learned this technique from an old gunsmith who let me watch him on numerous occasions and years later I helped him by giving him strips of 1075 annealed which is all I have ever used.I am not claiming perfection but I have sent locks all over and never was concerned about springs.Doing the same thing over and over again probably has something to do with this as well/.
Bob Roller

[Dphariss]

I routinely re-arch  springs with a propane torch by polishing so I can watch the color, then bending with pliers or vise-grips to more arch and then heating till I feel the spring start to relax then stop heating and hold in place another 10-20 seconds. Its a good cure for a spring that is strong enough but does not have enough preload to give the desired power. I only heat to the color that a spring would be brought to in tempering. Going too far results in having the reharden the spring in most cases.