Over the years, I have managed to accrue a small array of AR15 recoil springs. I recently decided to measure their lengths and rates, in an effort to categorize them for future use. I made a spring rate measurement tool that I believe to be fairly effective. I measured the free length of a spring, put it on the tool, compressed it an inch, and then measured how much weight needed to be applied to compress it another inch. The free lengths and weights required to compress it that second inch are listed below.

10"/25.8oz
10.25"/25.8oz
10.75"/23.6oz
10.25"/23.6oz
10.5"/26.6oz
10.25"/26.6oz
11"/26.6oz

I have a few more in rifles that I have yet to record the lengths on, but did get the weights; I'll add them later:
11.5"/26.6oz
10.5"/25.8oz
10.5"/23.6oz
9.5"/39.9oz (.308 carbine-length spring)

They're all "in spec", length-wise, but some are perhaps on the weaker side of things. I have never put enough rounds on any one spring, to make one weaken to any significant degree, but a couple of those springs are from LE surplus guns of unknown history.

This message has been edited. Last edited by: KSGM,

It is worth mentioning, in connection with suppressor tuning discussions, that the .308 carbine spring is in a Colt 933, with an H3 buffer, gas buster CH, and Gemtech carrier, and it still isn't as pleasant as either of my other suppressed builds, which have more of a focus on gas port size and gas venting. This is likely due to the gun being gassed-up from the factory, combined with it's previous life as an LE rifle. Despite it's zany ingredients and sub-par performance, I am hesitant to dismantle it, as I've had it for quite a long while, and it has proven very accurate for me.

If it's over gassed you could try a Black River Tactical gas tube and slow it down.

I just got one in to calm mine down a bit.
I'm not running suppressed but still want it gassed right.
As is with the 0.081" gas port I'm needing an A5H4 buffer with 5.56

Using the drop down selections and letting them select the port size got me a 0.076" one to use with a Tubbs flat wire spring and A5H2 buffer.

A set screw installed in the gas block and drilled for the proper size would last longer but require removing the gas block.

Thank you for reminding me about that! I had learned about them in a discussion on the suppressed weapons forum, but I never had the thought to apply one of those tubes to that particular gun. I ordered one just now!