Question about carbine length vs mid length

sroc112

sroc112

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Feb 17, 2024
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#1
Assume all else the same - you have 2 uppers, one is carbine length gas system, one is mid length, 16 inch barrels in 5.56.

If you wanted to use one on a close quarters AR build with a red dot, and one on more of a medium distance range toy with an LPVO, would you have any preference as to which rifle got which upper? Either one perform any better for longer distances vs close quarters?
 
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#2
I don't see any correlation between intended use and gas system length. I can't see any scenario regardless of target distance that I would want a less smooth running gun.

That said, 16" RLGS 5.56 barrels are a bit rare and I wouldn't recommend them to someone unfamiliar with gas gun tuning and troubleshooting.
Intermediate is the best of all worlds for any user.
 
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#7
oldrifleman said:
All my 14.5” barrels are Mid length
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They probably shoot softer and have less wear and tear as well.
My only point was the carbine length gas isn't particularly we'll suited for a 16" barrel.
All can be tamed and adjusted with buffer and carrier weight and adjustable gas systems but that can be mostly avoided.
 
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#8
The difference between the two is dwell time. That is the length of the time period during which gas is being dumped into the action. Although there is nothing "wrong" with a 16" or 14.5" barrel with a carbine length gas system, it can be argued that longer barrels with carbine length gas systems suffer from an excess of dwell time. What this means to the shooter, especially if running suppressed, is more gas, a more violent cycling of the action and a bit more difficulty for tuning to operate well in a larger window of operation.

A mid length gas system will run more smoothly and less violently, making for a more pleasant shooting experience and more longevity of parts.

In short, mid length is better for 14.5 or 16" barrels. When you get to shorter barrels, mid length gas systems will exhibit problems associated with too little dwell time.
 
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#14
RUTGERS95 said:
under 16 I prefer carbine and this has zero bearing on felt recoil

placebo effect strong here with the hive :)
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Lol. We've been over this before. It's easily tested, and it's easy to measure and graph the increased recoil of a CLGS. Then there's parts and brass wear and tear that is well documented.
 
#18
RUTGERS95 said:
we have and I'm not wrong

move on
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What are your testing methods? Full auto fire? Slow mo video? Recoil sleds? Recoil pendulums? Measured pairs? Triples? Because all of that has been ad nauseum and the results have always been conclusive. You may be the last person on earth still arguing against all that testing.
Hell, I was just at a retirement party with a rental select fire lower with two uppers being swapped back and forth to allow cooling. Identical shit spec uppers but one MLGS and one CLGS.
You could watch all dozen people nearly shoot the range ceiling in a burst with the CLGS and only get half as high with the MLGS.
 
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#19
"close quarters", meaning it could theoretically be used as a weapon some day, God forbid?

ME, just based on uppers I've personally owned, I'd trust the mid length more for that. The only one real problem child I owed was carbine length gas.
 
#20
sroc112 said:
Assume all else the same - you have 2 uppers, one is carbine length gas system, one is mid length, 16 inch barrels in 5.56.

If you wanted to use one on a close quarters AR build with a red dot, and one on more of a medium distance range toy with an LPVO, would you have any preference as to which rifle got which upper? Either one perform any better for longer distances vs close quarters?
Click to expand...

For what you're talking about it doesn't really matter a whole lot, my preference is mid gas on the 16", it seems to run smoother with some of my handloads. If you are in a free state consider a pistol upper for your "Close Quarters AR Build" I've got a cheap 11.5 that I really enjoy shooting.
 
#22
The shorter the barrel and the more it will run suppressed the more likely I am to convert it to piston.

There are some great conversion kits out there that tune and gas out forward really well.
 
#23
A big thing to consider is that the only reason we ever had CLGS 16” was due to NFA.

The CLGS was originally adopted for the Colt 607 Commando in the CAR-15 family of weapons for Colt.

iu


It was also used on the Colt 608 USAF Survival Weapon:

iu


When they went to mass-produce, they updated to the Colt 609 & 610, which had problems with plug dwell, so they went to the 629/XM177E2 11.5” with 4.5” moderator:

iu


ATF actually interfered with Foreign Military Sales with restrictions on exporting silencers, and the retards at FTB considered the 4.5” moderator a silencer, so XM177E2 FMS was banned, and the Colt 653 with pencil 14.5” barrel was type classified as the M16A1 Carbine:

iu


For the civilian market, Colt introduced the SP-1 Carbine Model R6001 in Sep of 1977, complete with its Mafia/ATF-compliant 16” arbitrary length barrel:

iu


Colt actually developed a MLGS Carbine back in the 1960s and prototyped it, but it never went anywhere at the time. KAC has one in their museum. It’s over on the right side of that wall or the other wall mostly out-of-frame.

iu
 
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#29
Cascade Hemi said:
The 14.5" is for bayonet compatibility.
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There was something I saw in the past few years that said they increased barrel length until the plug dwell time worked reliably since the back pressure from the 4.5” moderator was taken away. It was apparently a happy coincidence that it lined up with the M7 bayonet. I’ve heard different things over the years.

The 653s feel like pistols compared to most of the modern iterations of AR-15s over the past 30 years.
 
#30
Just a quick search for port and chamber pressures at different port locations yields a lot of information. I’m not sure how accurate the info in this chart is or their test procedures.
IMG_6696.jpeg
 
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#31
RUTGERS95 said:
under 16 I prefer carbine and this has zero bearing on felt recoil

placebo effect strong here with the hive :)
Click to expand...
Man, I usually take the position that everyone is entitled to their opinion, but a statement like that just adds to the heap of misinformation that the internet is already flooded with. Of course you could be right. You may have tested under conditions that I dont have access to. As I understand it, the laws of physics differ in the twilight zone.
Cascade Hemi said:
For the most part but they'll run unsuppressed.
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Can you please qualify this? I mean, a V8 will technically run with 2 spark plugs missing, but it is far from ideal.

Are you running flow through cans or conventional? And you're getting a satisfactory closed bolt lock time either suppressed or unsuppressed? Are you swapping out buffers?

Im asking because I'm getting ready to send a midlength gas barrel in to get chopped to either 11.5 or 12.5 and can't decide. My intention is to control gas with a riflespeed.
 
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#32
TonyTheTiger said:
Lol. We've been over this before. It's easily tested, and it's easy to measure and graph the increased recoil of a CLGS. Then there's parts and brass wear and tear that is well documented.
Click to expand...
wouldn’t gas port size come into play there for the carbine length?

i have an FN 16” carbine length that is ported very well and behaves better some midlengths, that were not.
 
#33
TonyAngel said:
Man, I usually take the position that everyone is entitled to their opinion, but a statement like that just adds to the heap of misinformation that the internet is already flooded with. Of course you could be right. You may have tested under conditions that I dont have access to. As I understand it, the laws of physics differ in the twilight zone.

Can you please qualify this? I mean, a V8 will technically run with 2 spark plugs missing, but it is far from ideal.

Are you running flow through cans or conventional? And you're getting a satisfactory closed bolt lock time either suppressed or unsuppressed? Are you swapping out buffers?

Im asking because I'm getting ready to send a midlength gas barrel in to get chopped to either 11.5 or 12.5 and can't decide. My intention is to control gas with a riflespeed.
Click to expand...

i’ve cut a couple midlength 16’s and 14.5’s down to 12.5 and left the port alone and they were perfect for ejection pattern unsuppressed.

putting a can on those just needed to up the buffer one weight.
 
#34
TonyAngel said:
Man, I usually take the position that everyone is entitled to their opinion, but a statement like that just adds to the heap of misinformation that the internet is already flooded with. Of course you could be right. You may have tested under conditions that I dont have access to. As I understand it, the laws of physics differ in the twilight zone.

Can you please qualify this? I mean, a V8 will technically run with 2 spark plugs missing, but it is far from ideal.

Are you running flow through cans or conventional? And you're getting a satisfactory closed bolt lock time either suppressed or unsuppressed? Are you swapping out buffers?

Im asking because I'm getting ready to send a midlength gas barrel in to get chopped to either 11.5 or 12.5 and can't decide. My intention is to control gas with a riflespeed.
Click to expand...

11.5 MLGS will run unsuppressed but has to be gassed for it. If you want it to run both suppresses and unsuppressed correctly, you need an adjustable gas block. You could gas it for unsuppressed and use a flow through, I haven't done that though. With a regular suppressor and a H1 buffer, you only need a .057 gas port.

Most of your questions don't make sense. 11.5" MLGS works, I have posted all of this information before and you're welcome to search for it.
 
#35
tucaz said:
wouldn’t gas port size come into play there for the carbine length?
Click to expand...
Absolutely, up to a point. Port size controls gas volume, but does not dictate gas pressure. Both volume and pressure add to recoil. A mildly gassed CLGS could easily be softer than an overgassed MLGS. But if you compare apples to apples, the longer system will always be softer.
To really illustrate it, you could take a CLGS and a RLGS, drill the port to .110" or whatever the ID of a gas tube is, making them as fully gassed as possible, and the RLGS will be significantly softer. Put AGB's on those barrels, choke them down to the edge of function, and even when they're both barely locking back on empty the CLGS will be snappier.
Dwell time plays into this as well, an CLGS 18" barrel will have more recoil than a 12.5" CLGS barrel.
 
#36
TonyAngel said:
Man, I usually take the position that everyone is entitled to their opinion, but a statement like that just adds to the heap of misinformation that the internet is already flooded with. Of course you could be right. You may have tested under conditions that I dont have access to. As I understand it, the laws of physics differ in the twilight zone.

Can you please qualify this? I mean, a V8 will technically run with 2 spark plugs missing, but it is far from ideal.

Are you running flow through cans or conventional? And you're getting a satisfactory closed bolt lock time either suppressed or unsuppressed? Are you swapping out buffers?

Im asking because I'm getting ready to send a midlength gas barrel in to get chopped to either 11.5 or 12.5 and can't decide. My intention is to control gas with a riflespeed.
Click to expand...
crane tested and said immaterial wear and the measure of impulse recoil would not affect shooter. buffer set up has more to do with felt recoil than mid vs carbine

arfcom has so much on this validating with govie tests it's surreal. Hell a research on this site will have the links and pdf to testing as i've seen eons ago.

you don't even need to be intelligent to look at the numbers to understand that you simply will not really 'feel' the difference. we're talking hit a fly or nat on your windshield here.

the laws of diminishing returns apply to this and the results of the Crane and Abby testing
 
#38
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#39
RUTGERS95 said:
you don't even need to be intelligent to look at the numbers to understand that you simply will not really 'feel' the difference. we're talking hit a fly or nat on your windshield here.
Click to expand...
Who can't feel the difference? The average gun owner? The average infantryman? Sure, I buy that. I have yet to meet either of those who can tell if the bolt chambered a round based on the sound. Or know the gun malfunctioned before the they pull the trigger and get a click, because they felt something weird.
But literally every regular shooter I've handed two identical guns to, one CLGS one MLGS, after shooting both in an unwitting blind test, asks why the one sucks to shoot in comparison to the other.
 
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#40
I notice pretty significant differences between 20” RLGS (very smooth), 16” MLGS, and 16” CLGS.

I put a MGI Rate-Reducing Buffer in my 727 look-alike though to dampen that snappy CLGS feel.

Port diameters are different on them or can vary a lot.

A CLGS 16” AR-15 ported to run Wolf trash reliably will be pretty snappy with M193 and M855.
 
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#41
TonyTheTiger said:
Absolutely, up to a point. Port size controls gas volume, but does not dictate gas pressure. Both volume and pressure add to recoil. A mildly gassed CLGS could easily be softer than an overgassed MLGS. But if you compare apples to apples, the longer system will always be softer.
To really illustrate it, you could take a CLGS and a RLGS, drill the port to .110" or whatever the ID of a gas tube is, making them as fully gassed as possible, and the RLGS will be significantly softer. Put AGB's on those barrels, choke them down to the edge of function, and even when they're both barely locking back on empty the CLGS will be snappier.
Dwell time plays into this as well, an CLGS 18" barrel will have more recoil than a 12.5" CLGS barrel.
Click to expand...
ya true. rifle length gas is the obvious comparison, super soft.

i’ve just never played with CL and ML to that extent as you suggested.
 
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