16" Barrel, mid length or Carbine gas?)

[MSplumber]

Don't forget the huge test NSWC-Crane did in 2018 comparing CAR vs MID length gas on 14.5" M4A1s.

The MID length has significantly higher reliability numbers.

https://www.m4carbine.net/showthread...-VS-MID-LENGTH
https://partner-mco-archive.s3.amazo...1527866983.pdf

There are several things that make me raise an eyebrow at this test.

1. What state were the standard M4A1 rifles/uppers in? Were they brand new production, or were they just used guns taken off the rack? Previous military tests have been notorious for using clapped out old M4s (ie, the sand tests in 2007)
2. They were using M855A1, an insanely high pressure round. Compared to reliability figures done by the Army in 2009 showing the M4A1 having 3600 Mean Rounds Between Stoppages in a baseline reliability test, even the midlength in this test did rather poorly. Many government weapons contracts require at least 2000 MRBS. How would this test have gone if they were using a round that the weapons were actually designed for that isn't damn near proof pressures, rather than one that isn't compatible with any of our NATO allies' rifles and even many of our own (M27 IAR)?
3. Non-military are not using M855A1. I suspect that in certain conditions with certain ammo (.223 pressure), the 14.5" Mid could possibly be undergassed under certain circumstances. Granted, that's just speculation on my part.
4. They should've tested the CHF barrel variable and midlength gas system variable separately. Was the longer barrel life due to the gas system length or the CHF barrel? Or some combination? If so, to what degree each? Testing them separately could've told us that.

Personally I have experienced some midlengths being a little more picky on ammunition, with a 14.5" Midlength BCM not being able to reliably run quality brass case .223 (PMC Bronze that runs just fine in my carbine gas and rifle gas guns). And although it's slightly longer than Midlength, a friend's KAC also would not run .223 with acceptable reliability. BCM's statement that their 14.5" Midlengths are meant to be used with full power 5.56 NATO ammo seems to support this.

14.5" and 16" Carbine gas guns with proper gas ports (ie, a Colt LE6920 with a .0629" gas port) have proven to be extremely reliable. Considering many manufacturers hog out their midlength gas ports anyway, I'd take a properly gassed carbine length system like a Colt or LMT over most Midlengths, or a 20" Rifle Gas.

[xFREDx]

choose what you want. the middy will be a better shooting experience felt (depending on gas port size and other factors). the carbine will typically be more reliable as it is under a longer dwell time to pressurize the system. the M4's in the military have been fine as a carbine gas system. That is not to say the middies will not be reliable, we know for a fact they are reliable just stating what could be argued.

[1168]

Wow, the "Background" slides in the linked PDF are a hot mess. If I was briefing a study comparing carbine and mid-length gas systems, I would maybe mention gas tube length for one or both or explain what a mid-length gas system is. Instead, a rifle gas system length is provided and the audience left to guess at the other two.

The slides also refer to a "dwell distance" of 7 and 6.7 inches, which Lysander has identified as incorrect usage of the term.

On a personal level, I vote for mid-length over carbine for 16" barrels, but would buy a Colt 16" carbine barrel before a PSA 16" mid-length.

Andy

Yes, they are literal garbage, as many of this type are. See also: Overmatch

[AndyLate]

choose what you want. the middy will be a better shooting experience felt (depending on gas port size and other factors). the carbine will typically be more reliable as it is under a longer dwell time to pressurize the system. the M4's in the military have been fine as a carbine gas system. That is not to say the middies will not be reliable, we know for a fact they are reliable just stating what could be argued.

There is zero evidence a 16 inch midlength is less reliable than a 16" carbine. It is not "what could be argued" it is not true.

A quality 16" carbine is absolutely no more reliable than a quality 16" midlength. There is no advantage to buying a carbine gas 16" gun over a midlength.

Andy

[Red*Lion]

I have 16" AR's with both. I see no big difference between them, at least to me there is not enough difference to matter. Either will work fine.

[HKGuns]

I may be wrong in my thinking, but I buy 16” barrels with mid length gas set ups.

Carbine gas was developed by Colt for the 14.5” barreled M4 and the port pressures are higher than necessary for a 16” civilian barrel.

Either will work, obviously, or you would hear all sorts of issues with LE6920’s with carbine gas systems and you don’t.

I assume the lower pressure and hence lower bolt velocity of a 16” mid length setup is easier on the moving parts. The gas is also cooler at that length which may also decrease the stresses on the components.

I usually try to match the gas system to the barrel length.

14.5” or shorter Carbine
16” Mid length
18” Rifle
20” Rifle

This is how I do it, right or wrong. You can choose to do it differently and it will likely work just fine.

[17K]

I do agree that the mid length is a better mousetrap on a 16” barrel, but done right, a carbine is pretty dang good. I’ve ran a bunch of 16” Colts over the years, the last two to well over 15K rounds with no parts breakages or malfunctions attributable to the gun.

[GH41]

I have 16" AR's with both. I see no big difference between them, at least to me there is not enough difference to matter. Either will work fine.

THIS ^^^

[MSplumber]

I love the old Colt AR's like the Colt Sporter HBAR's!!!!!!!
I have a premium PSA with a 16" FN barrel and I love the quality!!!!!!

Is this a joke?
I'd take a new production Colt 6920 over any PSA any day.

[1168]

My Premium PSA upper has a CHF 16" FN barrel. a Toolcraft bcg, runs like a sewing machine, and will shoot 1 hole groups at 100 yards all day long with Australian Outback 69 grain sierra match ammo. It was 1/2 the price of a Colt!
I also have a Taurus G3 pistol for the same reason and it also runs like a sewing machine. I use Sprinco Machine Gunners Lube on all my guns now! So put that in your pipe and smoke it!!!!!!!!!!!

How much is a Colt in your area?