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Posted: 7/18/2007 4:23:33 PM EDT
| Does anyone have the official spring constant for the AR buffer spring? |
| If your referring to the ft. lbs. of pressure the spring provides, I’ve never seen that type of data. There are min and max spring dimensions in the Unit And Direct Support Maintenance Manual M16A2, M4, M4A1 |
| You could figure it out for yourself pretty easy. Take the upper off, place the lower buttstock down on the ground. Put some sort of weight on the buffer, maybe a roll of dimes with a book balanced on top; look around and be creative. You just need to be able to measure how far the buffer is pressed back into the tube. Weigh the dimes and book to get your F. The distance the buffer is depressed is the X. Solve for your K. It doesn't matter that the spring is already compressed some b/c the spring constant is linear. |
I tried that, but the hammer kept getting in the way ... I couldn't get any appreciable weight on the buffer/spring and wanted to be able to get several data points ... so I dropped that route ... |
I didn't grab the AR out to try myself, though I did consider it. One data point is enough, but either way, good job for trying!  Edit: Idea #2. Pull the rear pin on your rifle and allow it to swing open. Hold it muzzle down by the buttstock and place your finger on the buffer. When you let go of the rifle its weight (minus the spirng and buffer) will be supported by the spring. My buffer isn't 100% vertical when I do this so there will be some inaccuracy, but that'll vary by rifle I guess. Note how far your finger sinks into the buffer tube for your X. The weight of the rifle minus the buffer an spring is F. I'd give you an estimate for K but I have no idea what my rifle weighs and I don't have a scale. |
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For my project, it is of importance ... the results Inputs Diameter of spring wire, d: 0.071 in Outer diameter of spring, Douter: 094 in Free length of spring, Lfree: 13.4 in Number of active coils, na: 37 Youngs modulus of material, E: 200 GPa Poisson ratio of material, n: 0.3 Density of material, r: 7500 kg/m^3 Answers Spring constant, k: 1.46 lbf/in Maximum load possible, Fmax: 15.5 lbf Maximum shear stress possible, tmax: 107 ksi Maximum displacement possible, Ldef: 10.6 in Length of wire required to make spring: 107 in Solid height: 2.77 in Distance between coils in free spring: 0.362 in Rise angle of coils: 7.56 deg Lowest spring resonant frequency, fres: 35.0 Hz Shear modulus of material, G: 76.9 GPa Mass of spring: 1.84 oz |
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