AR-15 Carbine Action Spring Performance Differences

In the past, I have used high speed video to analyze various aspects of AR-15 operation. Today, I did some testing at the range with several action springs. This is intended to be an ongoing test, so all three action springs were brand new. They are:

– Tactical Springs/Sprinco “Blue” recoil spring
– Brownells M4 Recoil Spring – Chrome Silicon
– Brownells AR-15/M4 Recoil Spring

The test weapon was a 16″ carbine gas AR-15 with a .063″ gas port, H buffer, 5.56mm NATO chamber, M16/Auto bolt carrier, and AR-15 fire control group. The bolt carrier group was cleaned and wiped down with a dry cloth before the test. Two types of ammunition were used, Prvi Partizan M855 and Federal XM193. One magazine, a Lancer L5 20rd, was used for the test, and it was always loaded to 20 rounds at the beginning of each string of fire, which consisted of five rounds.

Rate of fire calculation is based on the time it takes for the bolt carrier group to fire, unlock, extract, eject, cock, feed, chamber, and lock, plus the time it would take for a standard M16A1 fire control group to allow the hammer to fall once more. These calculations are therefore theoretical, but this method has always been verifiable when compared to actual M16A1 high speed video testing.

Rate of Fire

The rate of fire was highest with the Springco Blue action spring (726rpm M855/680rpm XM193), median rates of fire were achieved with the Brownells Chrome Silicon spring (685rpm M855/667rpm XM193), and the lowest rates of fire occurred with the Brownells AR-15/M4 recoil spring (656rpm M855/626rpm XM193). The differences in cycle time and bolt carrier velocity between the three springs were always noted during the feeding, chambering, and locking portions of the cycle of operations; put simply, the lower rates of fire came as a result of reduced forward bolt carrier velocity. As forward velocity fell, so did consistency.

Standard Deviation

Relative to the other action springs, the Sprinco Blue action spring was very consistent overall, with a total cycle time standard deviation of .55 for M855 and 3.03 with XM193. The Brownells Chrome Silicon spring was not far behind, with M855 and XM193 standard deviations of 1.87 and 3.81, respectively. The Brownells AR-15/M4 recoil spring could not be considered as consistent, with standard deviations of 5.59 and 12.87.

Further testing will be conducted.

16 thoughts on “AR-15 Carbine Action Spring Performance Differences”

    1. Depends. A low, inconsistent cyclic rate means that if a few factors are changed in an unfavorable manner, the weapon is more likely to experience a stoppage or malfunction. In this case, the bolt carrier group was sometimes slowing down considerably when it encountered the top round in the magazine. Of all the ways to lower the cyclic rate, this is among the least desirable.

  1. I’d like to see units on the two graphs, the first is of course RPM, the send, I’m assuming is milliseconds, but am unsure. Always better to label the axis, or axes when appropriate, and alleviate any ambiguity.

  2. Outstanding review. I know you have used (and liked) the Tubbs flatwire action spring as well. Also, would a Wolff XP spring fare better?

    Lastly, it seems that an action spring can be used to moderate the rate of forward return of the BCG/buffer assembly. Can buffer weight be used to moderate the speed with which the systems recoils to the rear?

    This is my favorite type of article. Keep em comin!!! :)

    1. I enjoyed the article too. In addition to Deputy B’s buffer question, would an H2 buffer (or heavier) improve the bolt cycling consistency?

      Also, will you be adding the Tubb’s flatwire spring into the mix? I’d love to see how it compares to the traditional round coil.

      Thanks, AT.

  3. Love these kinds of reviews even if my own knowledge is very limited. What would you say is the best setup? A low cyclic rate with very high consistency? If this is true, what is the best way to achieve this?

  4. Cool. Do you notice a general increase or decrease in cyclic rate as the internals heat up? Shouldn’t a larger round count be used if measuring consistency? Will you be testing buffer combos as well? Planning on testing the A5? What is the airspeed velocity of an unladden swallow?

  5. Isn’t the “blue” Tactical Springs recoil spring ment for lower power ammunition such as Wolf or .223 55gr bulk? Isn’t the “Red” spring from Tactical Springs, (Springco), the correct choice for 5.56, or full auto applications? This could be why the cycle rate is higher.
    The red spring is the one they recomended to me, anyway. Good review, love this stuff.

      1. According to Sprinco’s website White is their standard weight spring. Blue is enhanced and red is extra power.

        1. Looks to be a new spring. Before they only had blue and red. Both blue and white are listed as standard power. I wonder what the differences are.

          1. The white spring is a blue spring minus three coils. It is the brainchild of Mike Pannone.

  6. I would like to know one thing:

    If you put each into an AR lower upright on a digital scale, zero it, and push on the buffer until it moves 1 mm, how many lbs does the scale read for each spring? Then we could correlate spring load with the cyclic rates.

  7. Which spring and buffer would you recommend I get? Sprinco white or blue? Spikes T1 or T2 buffer?

    SPECS:
    14.7″ Mid-Lengh
    Gas Block: .750″
    Gas Port: .078″
    BCG: M16
    Good Mags

    Thanks,
    Chris

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