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BIG Freakin’ Cartridge Test 012: RUAG SS109 (M855 Equivalent) 5.56mm NATO, 16″ and 20″ Barrels

This article was originally posted on Thefirearmblog.com

Next up for the Big Freakin’ Cartridge Test is RUAG Ammotec’s version of the NATO-standard SS109 round (equivalent to US M855). I believe the ammunition I tested may have been made in RUAG’s facility in Thun, Switzerland, although I have not confirmed that.

Continuing on from the last installment, we are now looking at the velocity test results for the 20″ barrel (more on the 16″ later).

The test procedure was as follows:

  1. Condition ammunition to 70 °F +/- 5 degrees for at least 1 hr (in practice ammunition was always conditioned overnight).
  2. Mount chronograph to barrel or rail.
  3. Record the temperature in the conditioned container before each string.
  4. Withdraw one round of ammunition from the cooler.
  5. Load and immediately fire the round.
  6. Cool chamber back to ambient conditions for 30 seconds*
  7. Repeat steps 3 through 6 nine more times.

This procedure was followed for 14.5″, 16.1″, and 20″ barrel length velocity tests. To measure velocity, a Magnetospeed V3 chronograph was used attached to the barrels of the 16.1″ and 20″ uppers, and the rail of the 14.5″ upper. It needs to be noted that for all 16″ barrel testing, a cooling time of 10 seconds was used instead of 30, as it was becoming obvious that the additional 20 seconds were unnecessary. In the future, 10 seconds will be used for all barrel lengths.

The chronograph results for the 20″ FN chrome-lined CHF barrel are as follows (Shot #, followed by muzzle velocity in ft/s):

1. 3,095

2. 3,118

3. 3,078

4. 3,065

5. 3,094

6. 3,077

7. 3,126

8. 3,094

9. 3,080

10. 3,115

Which gave us the following figures:

Min: 3,065

Max: 3,126

Avg: 3,094

Standard Deviation: 20

Extreme Spread (highest minus lowest): 61

And the chronograph results for the 16.1″ Colt chrome-lined cut rifled barrel (Shot #, followed by muzzle velocity in ft/s):

1. 2,893

2. 2,936

3. 2,918

4. 2,955

5. 2,958

6. 2,940

7. 2,968

8. 2,970

9. 2,996

10. 2,949

Which gave:

Min: 2,893

Max: 2,996

Avg: 2,948

SD: 28.8

ES: 103

Once again, the 20″ barrel proved more consistent (somewhat) than the 14.5″ barrel, but interestingly the 16.1″ barrel was less consistent. This does mean that, for all 6 rounds tested so far, the 20″ barrel has in every case produced more consistent numbers than the 14.5″. However, in some cases, this difference has not been very massive, and perhaps more interestingly the 16.1″ barrel has not always been in-between the two, sometimes (as in this case), being significantly less consistent than either.

You knew there was a military feed lip gauge for magazines, right?

‘Mah Problemsolva’: Yup, it’s an RMR cut, suppressed and customized Hi Point C9