View Full Version : Testing Semi-Auto Pistol Springs

May 31, 2010, 08:52 PM
The next purchase I am going to make is a semi-auto in 40sw. I would like to record the factory spring length and rating and also know the actual spring length and strength of any after market spring I might install or try. And then also to retest later to make sure that the springs are still "up to snuff" if and when I want.

My first question is how are semi-auto springs rated. I am familliar how springs are rated for race car's and I think the process is simillar but after several attempts at searching Google and this site I did not come up with an answer I was confident with.

My other question is are there any reasonably priced instruments for testing these springs available and where I might purchase one. I searched Midway with no success.

I appreciate any responces.
Thank You,

May 31, 2010, 09:01 PM
My first question is how are semi-auto springs rated.
Springs are rated by the amount of weight it takes to compress the spring 1".

The tool for measuring it is called a scale.

Crisis (singular), crises (plural).

May 31, 2010, 09:07 PM
Thanks Scorth.

Is that the first inch of compression or after a preload and then test the next inch.


May 31, 2010, 09:10 PM
IIRC, it's the first inch.

Jim Watson
May 31, 2010, 09:26 PM
Firearms springs are rated on the load required to compress them to the working length in the gun. The mechanical engineer's spring constant is per inch, but for a 1911 the catalog rating is the total load to compress from the free length to about 1 5/8".

I realize this is contrary to Scorch's definition, but MY 1911 recoil springs do not take 16 lbs to compress one inch.

There is a recoil spring tester but it is rather expensive unless this is a major project.


I have seen assorted homemade versions. All you really need to know is the compressed length and figure out a way to stop travel of your tester at that spot. The one described at
says the compressed length is 1.625"
Elsewhere I have seen numbers from 1.46 to 1.81"

May 31, 2010, 09:44 PM
Thanks Jim and Scorch,

Jim if I understand corrrectly I need to know the spring length when in full battery, then know the action travel and test the strength to the difference. This is doable.

$80.00 for the tester linked to is something to consider. I also have some ideas for making my own with stuff I already have.

I will check back tomorrow if there is any more input.
Again thanks,

June 1, 2010, 12:57 AM
jt, 6/1/10

I also have wondered how springs are rated and was interested in measuring recoil spring tension in new springs and then later on after heavy use, especially when it came down to the springs in my 1911 Springfield ultracompact which went through recoil springs quickly.

My answer was to get a six inch long, 1/4" thick bolt and drill a hole in my work bench just big enough for the bolt to fit. I then put a flat washer on the bolt and put the bolt through the spring and into the hole in the work bench. I then flipped my portable postal scale upside down and compressed the recoil spring to full compression and recorded the values. The recorded values were always within one pound of the new coil spring rating. I also use the same technique to check my Ultracompact mag springs.

I know the above method is low tech, but it works and is cheap (as am I, but that is my parent's fault). Good luck.

best wishes- oldandslow

June 1, 2010, 06:39 AM
There's a very simple technique. Replace the recoil springs every 5000 rounds. They're cheap, easy to do, and take no skill. Don't get inventive stick with factory ratings. See http://www.gunsprings.com/1ndex.html

I keep spares for all of mine. Test for reliability before carrying.

June 1, 2010, 08:00 AM
1911rocks, 6/1/10

The advantage of knowing your springs new and used compression measurements keeps you from blindly replacing springs in the event of a malfunction. I too replace springs on a routine schedule but that routine varies by pistol size and type (for instance compact .45's, especially 1911's, need more frequent recoil spring changes). Knowing which recoil or magazine springs have lost compression compared to their new rating makes it easier to diagnose and fix a problem.

best wishes- oldandslow

June 2, 2010, 06:27 PM
Jim, I did not understand you correctly the other night. I need to compress to the working length from the free length and use that measurment of strength.

I do not know if I wil ever wear out a spring if they last 5,000 rounds but you never know. The reason I am inerested in this is I am planning to use 2 loads one with light load and bullet for practice, plinking and maybe IDPA competitions and the other with heavy bullet and max load for side arm when hunting. Maybe I am over analyzing but it seems like I may need 2 recoil springs for best operation. My common sense tells me that the factory spring will probably be optimized for something in the middle.

Thanks for all the responses. When I actually get my hands on whatever I purchase and do some experimenting I might have another question.