Reducing or "weakening" strength of "V" spring?

[Naphtali]

A query several months ago appeared to show that reducing the strength of a "V" spring was risky at best. Anticipating no one has a gunsmith whom he would recommend to do such a reduction, would leaving the hammer at full cock - stressing the spring - for several weeks, or several months, have the weakening effect I seek?

[D. Taylor Sapergia]

No.  Reduce the spring's power, if you really feel it necessary, by thinning it's thickness - not its width.  A little does a lot.

[Nate McKenzie]

And keep your scratches or tool marks running parallel to the length of the spring.  Cross wise marks create a score to start a break.

[D. Taylor Sapergia]

It is my observation that most commercial locks available to us today, do not have mainsprings that are too strong.  But some locks have springs that are not balanced!!  The mainspring and the frizzen spring must be balanced, for best lock function, flint life, and other factors.  A good portion of understanding this concept must come from experience.  It is not something that is easy to describe.

[D. Taylor Sapergia]

This thread could easily be moved to "Gunmaking" forum.

[Chris Treichel]

I have had to do this to a number of Indian made locks. The likes of which look like they should have been on a Buick. Just use diamond files and keep testing it until it is what you want.

[westbj2]

There are a number of variables involved in balancing a mainspring.  Broadly spreaking, if the lock geometry is correct, the lower limb of the main spring will be arrow straight at full cock. 
Another "must" is that the spring should taper UNIFORMLY both in width and thickness.
No need for special files, you should be able to readily file a properly heat treated spring....it will sound slightly different than mild steel and cut differently but still easy to file.
Initally it is safest to use the lock to determine where to take material off the spring. 
With some experience you will be able to look at the spring and get very close.....then use the lock to fine tune.
You can also use a spring vise to determine where to take off much of the material needed to balance the spring.
Jim

[ddoyle]

Jim, Can you expand on the use of a spring vise to determine where to take off material?

THanks

[westbj2]

Using a spring vice to balance a spring also takes a little experience so try it on an old spring first.
When cramping the spring, the feet on the long bar of the vise should be on the lower limb with one foot as far toward the tumbler hook as possible.  It is beneficial to have the style vise that has the sliding lower limb.
Put the spring in the vice and cramp it to about 25% of its final compression....study the lower limb carefully.....it should have a uniform and consistent arch.  If you notice a "flat" spot adjacent to a significant arc change, that area needs attention and likely careful thinning in thickness. 
(width taper should be already uniform and i like to think of width as the roughing out part of getting a correctly shaped spring with thickness as the fine tuning)
Proceed to 50% compression and repeat the above sequence.  If you feel confident then go to 75% compression and repeat again.
Finally put the sping back in the lock and study it further for possibly more thinning and tuning.
Why the emphasis on an arrow straight spring?  The straight lower limb at full cock indicates that the limb is working or flexing over its entire length.  A spring with a hump or bow  is telling you that it is working harder in one area than adjacent areas.....over time it will work harden in the problem area and be subject to failure.
A good stating place, even before picking up a file, is to study the shaping of a high quaility antique mainspring.
Jim