Spring Tension vs gunsmith

[CB45]

So I hear many people talk about reducing spring weights by shortening the spring. I.e cutting off coils. (Typically recoil spings) I am just confused by this. I'm not a genius, but reducing the number turns in a coil spring increases the force it takes to compress. I know it sounds backwards, but that's how it really works.

Anybody have experience reducing spring tension in this manner? The theory says it doesn't work, but what say you INGO?

 

[kludge]

For a given length of spring, yes you are correct. Theoretically.

Over short disances of long springs the spring constant is more or less "constant". The trigger spring is not "long" however.

Two things are occuring:

Spring rate is not perfectly constant as it is in the physics books. A coil spring is essentially a coiled up torsion arm, and the spring rate increases with increased amount of twist on a torsion arm.

Cutting a turn off the spring keeps the same spring rate, but also shortens the spring. This allows the spring to expand a bit (if you don't cut off too much it will still be under compression. Then with the lever advantage of the trigger on the spring and reduced twist on the torsion arm, so to speak, the spring rate is effectively reduced.

 

[kludge]

One more...

Assume you have a truly constant spring rate of 10# per inch. To compress the spring one inch you have to put 10# force on the spring. Two inches = 20#, 3 inches = 30#, 4 inches 40#, and so on.

Now lets take that spring, compress it two inches and stick it in a gun between the frame and the trigger. The gun is applying 20# of force to the spring. When you squeeze the trigger, as soon as you start to squeeze the trigger, you have to apply the force that frame/trigger was, just to start to compress it any more... so that's 20# of force from your finger.

Now let's just say that you have to pull the trigger 1" to fire the gun. At the end of the trigger pull you are now applying 30# of force.

Now let's cut a few turns off the spring and make it so that you only have to compress the spring 1" to get it to fit in between the frame and trigger. The spring constant hasn't changed, just the length of the spring. Now when you start your trigger squeeze you are applying 10# of force. At the end of the trigger stroke you are applying 20# of force, reducing trigger weight by half at the beginning and 1/3 at the end.

 

[Patternpimp]

Kludge is correct with his explaination on the application of force of a linear spring rate.

 

[CB45]

Thanks for the replies. That helps me wrap my head around the idea.

Chad

 

[billybob44]

Extra Springs..

Bottom line is--get yourself some spare springs BEFORE you start cutting coils off of your springs!! HA..Bill.