In researching my first upper build, I wonder if there is an advantage of one over the other. I generally prefer mid-length, but I don’t have a real reason. I notice the carbine length seems more common when looking at barrels. Is there a reason to choose one over the other in a 16” barrel length?
Mid-Length vs Carbine Length Gas System
- Thread starter DMW1116
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troy fairweather
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Mid, carbine is more for 14.5" barrels
Hugger-4641
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Most m4 clones kept the carbine length gas system though they have 16" barrels as opposed to the 14.5" barrel of the m4. That's why the carbine length gas systems are more proloific.
jonnyc
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Have/Had/Used both and haven't really noticed any particular difference or benefit of one over the other.
What would you use for a SPR upper?
Varminterror
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The difference between carbine and mid is grossly exaggerated online.
But… eh, since most barrels are notably overgassed, and since most folks don’t want to correct this with an AGB, lengthening out to middy reduces how obvious are the overgassing symptoms.
But… eh, since most barrels are notably overgassed, and since most folks don’t want to correct this with an AGB, lengthening out to middy reduces how obvious are the overgassing symptoms.
Riomouse911
Member
I have carbine, mid length, rifle length and piston uppers in 5.56.
Other than increased weight of the 20” HBAR rifle upper being different from my 14.5” and 16” guns, I really can’t tell much of a difference in recoil between the lot of them.
Stay safe.
Other than increased weight of the 20” HBAR rifle upper being different from my 14.5” and 16” guns, I really can’t tell much of a difference in recoil between the lot of them.
Stay safe.
I hadn’t considered that. Are adjustable gas blocks generally beneficial? I only have one on my AR-10 and wind up tweaking it for each load.
jonnyc
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I see them as just another fiddly bit that can go wrong. Handy if you're switching between sub and super sonic for a can, but not really relevant to 5.56.
Styx
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I agree... It's all over blown, exaggerated, and over analyzed. There's not much of a difference IMHO.
And typically there's no downside to mid gassed 16" barrel and there's plenty of them out there.
I have a WOA 16" mid gas SPR barrel and highly recommend them.
As to AGB I've put a couple on guns that are "supposed" to need them 300 BO and 308 AR10 and ended up just leaving them wide open.
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Styx
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Most AR15s are slightly over gassed for the same reason Glocks and other duty grade handguns have looser tolerances. It's so that they're still reliable with different ammo and under different conditions. It's not a bad thing unless it's to the extreme to where it's causing accuracy, reliability, or other issues.
I personally never fired a 223/556 AR15 that had recoiled to the point that it was worth even thinking about. It's a completely different story with a 12 gauge shotgun against the shoulder.
I personally never fired a 223/556 AR15 that had recoiled to the point that it was worth even thinking about. It's a completely different story with a 12 gauge shotgun against the shoulder.
I don't notice much of a difference when going from carbine to mid length with a 16" barrel. Now I do notice a difference between carbine and rifle length but part of that is also the longer barrel and the weight difference between a carbine and rifle.
Chuck R.
Member
IMHO it depends on the intended use.
For most purposes, no substantial benefit. Start running things on a clock, where split times start to count, and there's a difference. I can take my stock Colt LE6920 and run it against my 3Gun rig and it's night and day with the same loads. So by itself, not a big deal, add the other "stuff"; AGB, decent brake, lightweight BCG and the some of the parts is a world of difference.
For most purposes, no substantial benefit. Start running things on a clock, where split times start to count, and there's a difference. I can take my stock Colt LE6920 and run it against my 3Gun rig and it's night and day with the same loads. So by itself, not a big deal, add the other "stuff"; AGB, decent brake, lightweight BCG and the some of the parts is a world of difference.
Varminterror
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Quite relevant when a shooter doesn’t want their intentionally overgassed barrel to be overgassed.
As in an 18" barrel?
For that I like rifle gas systems with a 0.0995" gas port.
14.5" - 16" mid gas works well with a 0.076" gas port.
I use an A5 (A5H2 buffer) and A2 action with both.
Crane Naval did testing between mid and carbine gas.
Mid gas had less wear and tear on parts and lasted longer.
I thought there was enough difference that the carbine gas barrels are in a drawer and I just buy mid gas.
You have to do your homework and select a barrel that's ported correctly to start with or end up trying to de-gas it later, carbine or mid gas.
Some are ridiculously sized.
With an efficient gas system a 0.0625" gas port is more than sufficient for carbine gas.
One of mine is at 0.068" and SOTAR had one recently with a 0.089" gas port.
One mid I had has a 0.081" gas port.
I went the BRT gas drive route to reduce the gas in mine.
Now I look a little harder before I buy a barrel so I don't have to spend $70 later on to get the gas under control.
earlthegoat2
Member
In 450 Bushmaster applications,, carbine and mid length systems are recommended to Ben for longer barrel lengths.
I don’t really know why but have heard it from a few different sources.
Just some fuel.
I don’t really know why but have heard it from a few different sources.
Just some fuel.
Varminterror
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Here’s the skinny: 16” and 18” middies became popular due to what amounts to a popular misconception about how gas systems work. We all knew the history about the Dissipators, and everyone understands that the farther we go down the bore, the lower the bore pressure remains, meaning lower “port pressure.”
So folks assume the gas system pressure will be lower because the bore pressure at the farther port position is lower, and middies became popular…
BUT…
Folks neglect that the entire point of the port is to throttle gas - and not just throttle flow. Longer gas systems don’t necessarily ensure lower gas system pressure, because the PORT SIZE MATTERS. Restrictive orifices influence gas pressure drop across the port also, the tighter the port, the less pressure we have on the back side of the orifice, the bigger the port, the more pressure we retain on the backside. By design, longer and longer has systems also have bigger and bigger ports (also thicker barrels have bigger ports), and bigger and bigger ports have less and less pressure drop across the port - which means having lower bore pressure may not actually mean we have lower gas tube pressure. It’s a game of pressure AND flow impulse (dwell time, or duration of exposure). So it’s really just as common to have an overgassed midlength as it is to have an overgassed carbine length barrel.
As a shooter, I want control over how my rifle runs. As a builder, I give my shooters that control by using AGB’s. If we KNOW we will only shoot one load for a given barrel - one powder/burn rate, one bullet, one charge weight, at one ambient temp - then we can tune our port diameter ideally to our load. But if we decide we might run a light bullet over a fast powder sometimes and a heavier bullet over a slower powder, now we have lost control over how our rifle behaves. We do have the option to open our AGB to our lowest gas flow/pressure load and just leave it there, which is what most folks do, and then the overgassing with our highest pressure/flow loads is still significantly reduced vs. a plain block over the same gas port. But if you want control, AGB’s are cheap and easy.
So folks assume the gas system pressure will be lower because the bore pressure at the farther port position is lower, and middies became popular…
BUT…
Folks neglect that the entire point of the port is to throttle gas - and not just throttle flow. Longer gas systems don’t necessarily ensure lower gas system pressure, because the PORT SIZE MATTERS. Restrictive orifices influence gas pressure drop across the port also, the tighter the port, the less pressure we have on the back side of the orifice, the bigger the port, the more pressure we retain on the backside. By design, longer and longer has systems also have bigger and bigger ports (also thicker barrels have bigger ports), and bigger and bigger ports have less and less pressure drop across the port - which means having lower bore pressure may not actually mean we have lower gas tube pressure. It’s a game of pressure AND flow impulse (dwell time, or duration of exposure). So it’s really just as common to have an overgassed midlength as it is to have an overgassed carbine length barrel.
As a shooter, I want control over how my rifle runs. As a builder, I give my shooters that control by using AGB’s. If we KNOW we will only shoot one load for a given barrel - one powder/burn rate, one bullet, one charge weight, at one ambient temp - then we can tune our port diameter ideally to our load. But if we decide we might run a light bullet over a fast powder sometimes and a heavier bullet over a slower powder, now we have lost control over how our rifle behaves. We do have the option to open our AGB to our lowest gas flow/pressure load and just leave it there, which is what most folks do, and then the overgassing with our highest pressure/flow loads is still significantly reduced vs. a plain block over the same gas port. But if you want control, AGB’s are cheap and easy.
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ECVMatt
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My state does not like collapsible stocks or flash hiders. In an effort to comply, I have built a couple of rifles using 16" barrels, mid-length gas systems, muzzle breaks, and rifle length receiver extensions in conjunction with an A1 length fixed stock.
The end result is one of the smoothest shooting rifle configurations I own. The only one better is my 20" A2.
There is a huge difference between these rifles and my carbine gassed rifles. It could be the sum of parts, but I am a huge fan of the mid-length gas system and how it effects recoil on my rifles.
The end result is one of the smoothest shooting rifle configurations I own. The only one better is my 20" A2.
There is a huge difference between these rifles and my carbine gassed rifles. It could be the sum of parts, but I am a huge fan of the mid-length gas system and how it effects recoil on my rifles.
Chuck R.
Member
I built an 18" SPR using a WOA SPR fluted barrel, with rifle length gas and an SLR Titanium AGB. I'm very, very, please with how this rifle shoots.
FL-NC
Member
I finally got my first mid length a couple years ago- all I had used previously were carbine and rifle many years ago when I was issued a M16. I like the mid length- it seems a little milder to fire (not that the 5.56 is known for incredible recoil or blast). Of course, with shorter barrels like my 11.5 SBR or the 10" barrels I used in the mil, the carbine length is required.
CoalCrackerAl
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Varminterror
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@ECVMatt - what is the buffer weight you’re using in any of your carbine stocked rifles?
Most civilian AR’s with carbine buffer systems will have grossly underweighted Carbine buffers at only 2.9oz, whereas a Rifle buffer is 5.2oz. Kick in an H3 or Vltor A5H2 buffer at 5.3-5.4oz, and the difference in recoil impulse for the same upper on a carbine vs. rifle lower almost completely evaporates. The bigger trouble happens when folks have a grossly oversized port (intentional by barrel makers to ensure function) but then run a lightweight carbine buffer - these run, obviously, but they beat the hell out of themselves, just to avoid immediate customer service calls.
Most civilian AR’s with carbine buffer systems will have grossly underweighted Carbine buffers at only 2.9oz, whereas a Rifle buffer is 5.2oz. Kick in an H3 or Vltor A5H2 buffer at 5.3-5.4oz, and the difference in recoil impulse for the same upper on a carbine vs. rifle lower almost completely evaporates. The bigger trouble happens when folks have a grossly oversized port (intentional by barrel makers to ensure function) but then run a lightweight carbine buffer - these run, obviously, but they beat the hell out of themselves, just to avoid immediate customer service calls.
adcoch1
Member
I personally like middy gas barrels in 16" when using a conventional forend a lot more than a carbine length. I've never liked how short a carbine grip is. But as varminterror mentioned, it's port size, not so much location that matters. I rarely run adjustable gas blocks because I don't usually have problems getting any ar pattern rifles to cycle acceptably without them if the port size is reasonable. Only had one that HAD to have an AGB.
