Mean Rounds Between Stoppages for Colt 6920?

AR/M4 AR General Discussion
1

Does anyone have any data on the typical amount of ammo you can expect to get through a properly-maintained and cleaned Colt 6920 without a stoppage? Assuming regular cleaning has been performed.

The Crane tests of Mid Length vs Carbine show the carbine having 836 Mean Rounds Between Failures in ambient temperates, which seems very low to the point of being unacceptable. The Mid Length performed better, but still had a failure averaged every 1,993 rounds. I’ve seen where the Army supposedly said in 2009 that the M4 was having over 3,000 rounds between stoppages. This doesn’t make sense. I suppose the M855A1 used in the Crane test has something to do with it, but using regular M855 or M193, how many rounds between failures do you consider acceptable and what kind of number have you seen or are aware of in government testing (or even nongovernment testing)?

Personally, I think an AR should be able to go at least 2000 rounds between stoppages (again, assuming regular, proper cleaning intervals). I’m wondering if my Colt 6920 is capable of this.

Does anyone have any data on this?

2

16” 6920s are seriously overgassed

Unsuppressed especially shouldn’t have any issues running a good bit before a stoppage

Sent from my iPhone using Tapatalk

3

6920s aren’t overgassed by any means. If you have good mags, in-spec ammo, and a good preventive maintenance plan, there’s no reason it should ever malfunction.

I had a 6920 cut to 14.7" and it went over 15K with a couple of double feeds due to a wore out magazine. Had I rotated out that set of mags it wouldn’t have stopped once.

4

“Overgassed” is the new “low bore axis” I do believe. As long as your gun is assembled correctly, moderately clean, well lubricated, and using quality magazines & ammunition, it will run as well as it is capable of running. If you encounter a problem, document it & address it. Otherwise I wouldn’t worry about it.

5

It seems like, to some people here, “overgassed” is anything that gets more gas than it takes to barely cycle the action with full power 5.56 ammo in ideal, picture perfect conditions…

6

The Army tested all of the 5.56mm weapons with M855A1 ammunition in 2016, for the M4-types the reliability were:

M4A1 (new) - MRBS: 3592; MRBEFF: 6076
M4A1 (rebuilt) - MRBS: 3671; MRBEFF: 5758

In order to make a good comparison, on would need to know how many weapons were used, how many rounds per gun, cleaning schedule, rate of fire, magazine type.

The 2016 Army test used 6 new M4s, three Colt, three FN, six M4A1 PIPs, and six rebuilt M4A1, fired 6000 round through each gun as follows: four 30 round magazines between cooling, magazines one and three were semi-auto at 1 RPM, magazines 2 and 4 were full auto in 3 to 5 round bursts at 5 second intervals. After 600 rounds - wipe and lube, after 1200 rounds - disassembled, cleaned and measured. They used the Army’s new blue follower “Enhanced” magazines.

What were the Navy’s test criteria?

7

My 6920 was bending brass off the deflector when suppressed with a sprinco blue and H2 buffet . Had it cut down to a 13.7 and just run it “loud”

That’s what I call overgassed

Generally I tune them so without a can it ejects at 230-300 o’clock so it puts it at 130-200 when suppressed

The point of this post was overgassed wears parts faster…not enough gas will cause issues when dirty.

If the guns tuned right it’ll run without issue

Sent from my iPhone using Tapatalk Pro

8

The Army tested all of the 5.56mm weapons with M855A1 ammunition in 2016, for the M4-types the reliability were:

M4A1 (new) - MRBS: 3592; MRBEFF: 6076
M4A1 (rebuilt) - MRBS: 3671; MRBEFF: 5758

In order to make a good comparison, on would need to know how many weapons were used, how many rounds per gun, cleaning schedule, rate of fire, magazine type.

The 2016 Army test used 6 new M4s, three Colt, three FN, six M4A1 PIPs, and six rebuilt M4A1, fired 6000 round through each gun as follows: four 30 round magazines between cooling, magazines one and three were semi-auto at 1 RPM, magazines 2 and 4 were full auto in 3 to 5 round bursts at 5 second intervals. After 600 rounds - wipe and lube, after 1200 rounds - disassembled, cleaned and measured. They used the Army’s new blue follower “Enhanced” magazines.

What were the Navy’s test criteria?

Woah. That’s actually very impressive in my opinion. If military M4s are doing that with M855A1, I feel pretty good about the MRBS of my LE6920. As far as Crane’s criteria, this is everything I could find on it: http://soldiersystems.net/2018/05/14/nswc-crane-carbine-mid-length-gas-system-testing-shows-increased-performance/

Do you have a source for that test the Army did in 2016? I don’t doubt it, I’m just curious to see the details for myself.

My 6920 was bending brass off the deflector when suppressed with a sprinco blue and H2 buffet . Had it cut down to a 13.7 and just run it “loud”

That’s what I call overgassed

Generally I tune them so without a can it ejects at 230-300 o’clock so it puts it at 130-200 when suppressed

The point of this post was overgassed wears parts faster…not enough gas will cause issues when dirty.

If the guns tuned right it’ll run without issue

Understood. Yeah, mine ejects about 0230 or so. I’ve never shot it suppressed, though. From my experience I’ve never shot a suppressed AR that wasn’t overgassed. Seems like if it’s not overgassed with unsuppressed, it’s going to be overgassed when suppressed; and if it’s not overgassed when suppressed, it’s undergassed when unsuppressed.

I will replace parts at the recommended intervals for preventative maintenance for my 6920, so the faster parts wear doesn’t really bother me.

9

On a 16” I wouldn’t really worry about overgassing if your not running a can.

I only mentioned it because suppressed guns get FILTHY quickly

Faster parts wear is more an issue with the cyclic rate on 10” rifles than the 14.5 or 16

I’m your configuration let it overgas a bit and run it!

While not a 6920 my 10.3 is at 681 rounds all suppressed without cleaning and still running a top. Will probably clean it at 1k

Sent from my iPhone using Tapatalk Pro

10

For the everyday dude, I am not sure this is really anything to worry about so long as ypu use good magazines, good ammo and clean on a regular basis. I would presume that a 6920 should have a higher round count between stoppages as it is not running mags of full auto (unless you have one of those fun lowers).

11

Its not available on-line, but it’s the 2015 Re-Baseline Reliability Test 5.56mm Weapons using M855A1

12

Its not available on-line, but it’s the 2015 Re-Baseline Reliability Test 5.56mm Weapons using M855A1

How did you learn of this? I’d be really interested to read about that test’s findings in detail. Is there any way non-military can obtain this information since it’s not online?

I’m aware this might not be the most reliable source, but according to cited “weapons officials” in the Army, the M4A1 had 1691 MRBS.

“It’s still unclear how close any of the competitors came to reaching requirement 3,592 mean rounds between stoppages. Weapons officials did say that the M4A1, the special operations version of the M4, achieved 1,691 mean rounds between stoppages when it the tested using the new M855A1 ammunition.”

https://www.military.com/daily-news/2013/06/14/army-gun-makers-didnt-meet-reliability-standard.html?ESRC=sm_todayinmil.nl

Are you sure the 3,592 MRBS wasn’t the requirement for the Individual Carbine program rather than the actual recorded number of MRBS?

Strangely, I’ve also found a document from 2009 where the Army supposedly said the M4 was going over 3600 MRBS.
http://www.peosoldier.army.mil/docs/WeaponsReliabilityInformationPaper-Oct%2009.pdf

Since the IC program required a reliability rate higher than this number, perhaps they were using a requirement from before the M855A1 was adopted, which M855 was what the competitors designed the guns to shoot. That’s speculation on my part, though.

Overall I’m pretty confused. These numbers are coming from somewhere but are conflicting.

13

First, the 2016 report is the testing that established the baseline reliability for the M4/M4A1, the stated purpose of the testing was to establish that baseline, any potential replacement of the M4 had to exceed the M4 in reliability, namely 3592 MRBS. The date of the tests may have been earlier, the report I read was dated 2016. [EDIT: Yes, the tests were completed in 2006-07, the actual report is a list of every single malfunction that occurred, in every single weapon, over the course of testing, and a lot of test methodology.]

Second, 3671 MRBS is above 3600, if just barely. So, the PAO paper linked is truthful, but also a bit propaganda-ish.

And, last I heard the M4A1 is not “…the special operations version of the M4…”, at least not since 2012 when regular infantry units began fielding them. So, where did the article (dated 2018) get its info? And, is that info about pre-PIP weapons?

14

The 1691 MRBS number is said to have been given out by PEO Soldier officials from some rooting around. Not sure if it’s pre-PIP or not, or what magazines they were using.

I do see now where they established the baseline of reliability for the M4A1 at 3592 MRBS from this (on Slide 10): https://ndiastorage.blob.core.usgovcloudapi.net/ndia/2011/smallarms/PM_Soldier_Weapons_NDIA.pdf

I’m wondering if the 3592 number came from regular M855 and PEO Soldier’s 1691 came from after M855A1’s adoption.

This is not a primary source from the government, but according to this, the PMAG tests in 2015 with M855A1 had an MRBS of 4800. I’m looking for a government document showing that number: https://www.thefirearmblog.com/blog/2017/09/30/us-army-wants-13000-magpul-pmag-gen-m3-magazines/

15

I wanted to say thanks to Lysander for bringing the 2016 test results to my attention. It helped a lot.