Mid-length gas system in the cold.

[Disciple]

Split from another thread:

middies blow in the cold and will choke in sub freezing temps unless you open them up negating the the 'supposed benefit' of the middy. I say supposed because Crane testing was immaterial. Dissy has the rifle length for longer sight picture before dots were a thing. Has nothing to do with someone needing long arms

Trying to figure out the basis of this statement I found https://partner-mco-archive.s3.amazo...1527866983.pdf which I suppose is or is related to the Crane testing that was dismissed as "immaterial." Why is it so? It shows less malfunctions with a mid-length gas system than with a carbine-length gas system at low temperatures. At the same time a reduced cyclic rate was observed. Are there conflicting reports?

- 960 rounds at -60F for Reliability at Low Temp

-For carbine-length weapons, 27 out of 65 malfunctions occurred during low temperature testing. For
mid-length weapons, 16 out of 30 malfunctions occurred during low temperature testing. For low
temperature testing, carbine-length weapons had 333.3 mean rounds between failures (MRBF) compared
to 836.1 MRBF for ambient temperature testing and mid-length weapons had 562.5 MRBF compared to
1993.8 MRBF for ambient temperature testing. Approximately half of the total malfunctions recorded for
both carbine-length and mid-length weapons occurred during low temperature testing, so the relative rate
of malfunctions between carbine-length and mid-length remained similar to that of ambient temperature
testing.

- Averaged overall bolt speeds and differences in bolt speeds are presented in Table. The P-Values of
bolt speed results for both suppressed and unsuppressed fire are less than 0.05, so there is a statistically
significant difference between the two gas systems. Bolt speed is uniformly lower for mid-length gas
systems when compared to carbine-length gas systems. Mid length bolt speed was 2.13 fps, or 12.4%,
lower than carbine-length for suppressed fire and 3.23 fps, or 22.6%, lower for unsuppressed fire.

[ODgreenpizza]

The basis is critical reasoning isn't required for matriculation at Rutgers, and fudd lore from 90's that won't die.

[Todd.K]

It’s entirely possible to mess up the gas port size with any gas system. Some people are chasing “softest” without regard to cold or dirty function.

The comment about giving up the “supposed benefit” with a reliable port size mean's he was chasing an unrealistic combination of softest + reliable.

[lysander]

I would venture to speculate that many civilian ARs are "undergassed" in regard to military requirements.

[Wake27]

I heard literally zero complaints about the URGIs in the cold at my last unit FWIW.


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[HKGuns]

I would venture to speculate that many civilian ARs are "undergassed" in regard to military requirements.

Why would that be the case when for the last 10-15 years people are constantly jaw jacking about OVER gassed rifles from various companies. DD being one example.

Also, in the barrels samples I've personally gauged, obviously limited, but around 20 or so, a mix of C and ML...the Colt carbines were the smallest at .062/3 as my memory serves and the others were all larger with 16" middies varying widely between .068 and .082, again pulling from memory......

[Todd.K]

Most companies have figured out to leave a 14.5”-16” carbine at the military size. It’s the shorter barrels and mid length where testing may be less than robust and port sizes vary more.

Your example of middy port sizes go from “we make the softest middy ever” to “we know our customers shoot steel cased and forget to lube”.

Mid length will always be larger than carbine, and rifle will be larger than mid. Because the pressure in the barrel drops significantly over that length.

[lysander]

Obviously, a 14.5 with a 0.0625-0.0630 gas port will be up to military requirements . . .

But, most 16" mid-lengths I have will not reliably lock back when shot 180 degrees straight down, and these are the common available port sizes. That does not instill confidence if you start to factor in -20 degree performance.

[markm]

with a reliable port size mean's he was chasing an unrealistic combination of softest + reliable.

I have that gun. The 14.5 BCM Middy with ELW barrel is by far the softest and lightest AR I have and it's reliable. The "no free lunch" factor is the gunfighter muzzle device is barkie. No concussion like a brake, but it's louder for the shooter.

[pinzgauer]

for the last 10-15 years people are constantly jaw jacking about OVER gassed rifles from various companies.

Personally, I see gasport size as the new gas key staking trope for internet warriors to obsess about.

There is clearly a range on either end that creates problems. But a wide range in the middle that is acceptable with very nominal difference between them.

So clearly you can be grossly over gas or under gassed. That's not what I'm talking about... It's the folks who obsessed / jaw jack and wax eloquent on the forums about this non-stop.

Internet warriors love to argue/obsess about numbers and quantitative things.

But tend to miss qualitative things like metallurgy, dimensional specs, etc.

I was reminded of this at a LGS recently where a 17-year-old with acne behind the counter was lecturing me on how it was important to get the gas port to his favorite size down to the 1000th.

Yep, I know it makes a difference with suppressed, but a lot of that seems to be gas buster focused rather than operational.