Diameter of wire determine # lbs in rebound spring?

[H Richard]

I purchased a accumulation of S&W parts at an auction earlier this year. In it was a pretty good handful of rebound slide springs and J frame mainsprings. Is there a chart anywhere that tells what lb spring they might ve by the diameter of the wire?

A friend made a device to determine the weight of recoil springs for 1911's, and thinks he can adapt it to these much smaller springs, but if I could just measure the diameter of the wire it would be a lot simpler. (Or is there a better way?)

 

[TAROMAN]

I have measured many rebound springs, usually to sort them out.
Smaller diameter is lighter.
Didn't write down the measur ed ments, but, IIRC, .029 to .030 equate to the ltghter ones, about 13#

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[crandlewi]

You can calculate the spring rate yourself if you can fill in the blanks by looking at the spring. The formula for spring rate (lbs/in) is:
R= (Gd^4)/(8nD^3).

R= spring rate (lbs/in)
G = Modulus of spring steel = 11,500,000
d = Wire diameter
n = number of active coils*
D = Mean diameter = (O.D. of spring - d)

*the number of active coils depends on the configuration of the end coil on each end. If they are closed and ground flat than the number of active coils is the total coils minus the two end coils. If they are open and look like 1/2 a coil on each end then it is the total coils minus 1.

If none of this makes any sense to you than the alternative is to apply a force to the spring and measure the spring deflection. The force (lbs)/the deflection (in) = lbs/in spring rate.

I'm sure if you google "spring rate calculator" there are sites that let you plug in these numbers and spit out the answer.