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recoil springs


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There are several factors in determining the design weight of a 1911 recoil spring.

The below description is a rough method to determine the design spring weight.

You'll need a decent digital caliper to measure the wire diameter of the spring to be checked.

1911 recoil springs use music wire of .040" diameter up to .048" diameter.

.043" diameter is typically a 14# spring, .044" diameter is typically a 15.5# spring, and a .045" diameter is typically a 17# spring.

The recoil spring should be 6 inches long or greater. It should be made up of 30 or 32 coils. A recoil spring of 30 or 32 coils measuring less than 6 inches long is fatigued and is delivering less than the original as new spring rating.

A simple tester is a 9/32" hole through an elevated bar or board, with a 10 or 12 inch 1/4" dia rod running through the recoil spring to be tested. The 1/4" rod is threaded at the top to retain the spring with a washer and nut. The lower end of the rod is hooked to hold the hanging test weight. I use a small coffee can filled with 504, 180 grain lead bullets. This weighs 13 lbs. The recoil spring should suspend the weight with close to 2 inches of spring height. Add 40 more 180 grain bullets to raise the weight one pound. Continue to add in increments of 20 bullets (1/2 lb.) until the spring is completely solid. 624 bullets is 16 lbs. A weak fatigued 16# spring will compress solid well before you get to 16#.

7000 grains is one pound. Using different weight bullets just do a little math. I'm talking the bullet only, not including cartridge.

Hanging a known weight weight through any compression spring until it is compressed solid tells you what that spring is doing. It's simple.

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Yes a decent quality fish scale could work as well. By using a known weight this method isn't subject to the accuracy of any scale. Besides, I had bullets on hand, but no fish scale. I like the fact that both hands are free when using a known weight hung from the rod going through the test spring .

I weighed several bullets 8 or 9 at a time on my Dillon digital scale. I determined the bullets actually weighed 182 grains. I did the math and added the proper number of bullets to a small container hanging from the rod with the recoil spring above. If I had other known weights around the house I could have used them, such as barbell weights; I didn't.

Even scale test weights will work if they are easily available. I suppose a handfull of nuts or bolts would work as well, once the weight of each nut or bolt was verified.

A box of rocks, once checked on an accurate scale would work well.

The object is to have a known weight, verified by an accurate scale.

I found a close correlation with the test data and formulas used on internet spring engineering sites as well as the formula Joshua Smith presented in a spring post here about a year ago. See cutting springs.

It took me some practice to get used to running the formula after measuring the spring wire diameter with a digital caliper, then measuring the outside coil diameter as well as counting the number of active coils and measuring the free length of each spring.

Running the formula is not necessary to test any spring. I was interested in how my results correlated with the formula.

I was able to calibrate each of the 8 springs I had laying around as well as identify one fatigued spring that calculated out to be 16lbs but tested at just over 12lbs.

I'm now confident that this method will identify any 1911 recoil spring accurately.

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