Originally Posted by Chas1
Bart B, how do you know they are more than 10% less than their force rating. Is there a tool that measures this?
Yes, there's a tool. Most folks have a scale someplace in their house to weight themselves and as long as it's half way easy to read in the 25 to 30 pound range, here's how you do the task. Note this is a secret and you can't tell anyone else about it.
First, remove the bolt from the rifle and with it cocked then measure how long the firing pin is at its compressed length, write that number down, then remove spring completely from the bolt.
Second, secure a steel rod a bit smaller than the spring's inside diameter and half again as long as its uncompressed length to a flat piece of aluminum or steel. I've used a couple sections of the old M1 Garand cleaning rod. Weigh this spring holder on a scale, then write down its weight.
Third, with a flat iron bar about half and inch wide, a fourth of an inch thick and 6 inches long, drill a hole in it just barely bigger than that rod. This piece is now called your spring pusher.
Fourth, place the spring on the rod, set the rod's base on that (bathroom) scale, then place the pusher on the rod and let it come down to rest on the spring.
Fifth, push the pusher down until the firing pin spring compresses to the length it was in the bolt when compressed, then read the number on the scale's dial/beam/display (whatever). Again, write this number down (if you've got a short memory).
Sixth, subtract the weight of the plate and its rod(s) from the scale's reading at cocked spring length and the answer's what the spring's force rating is.
This is what I've done over the years. Others hang the rod from a support with a bucket attached to the pusher with wire (they know the weight of) then keep putting stuff in the bucket until the spring compresses to its "cocked" length. Then weigh the wired bucket, its contents and the pusher for the force in pounds needed. All sorts of Rube Goldberg inventions can be made to do this. A friend used a 1 gallon paint can with about 1000 military 172-grain match bullets in it for his 25-pound reference. When his 28-pound springs let that 25-pound weight compress his spring to its cocked length, he replaced the spring. It ain't rocket science. Just simple grade school physics. As long as the force needed to compress the spring to its cocked length can be measured, that's all that's important. And a 1 pound error from reality is fine.