AR15.Com Archives
 Whats the difference between 16" mid length and 16" M4 carbine?
Scvette01  [Team Member]
8/23/2011 9:43:34 AM
Any advantage between the 2? They are both 16", so what gives?
SGocka  [Team Member]
8/23/2011 9:44:48 AM
The length of the gas system.
Scvette01  [Team Member]
8/23/2011 9:47:28 AM
So the FSB is further forward then the M4?
What does that do for it
Medicfrost  [Team Member]
8/23/2011 9:49:48 AM
Oops, nevermind.
SGocka  [Team Member]
8/23/2011 9:56:07 AM
Mid length has a lower gas pressure. Makes for smoother cycling and is easier on your rifle because your BCG isn't slamming around so hard.
Scvette01  [Team Member]
8/23/2011 10:05:02 AM
Is the buffer the same as a M4 or is that different also

beprepared  [Member]
8/23/2011 10:28:27 AM
Same buffer, just smoother operation out of a middy vs an M4. Gas lube is 9" on a middy and 7" on an M4. With the extra real estate, your FSB is out further so you'll gain accuracy. Also, the dwell time is different (longer) with a middy vs an M4. I'd like to tell you about dwell time, but it is above my pay grade. From what I've read and comprehended, dwell time has to do with cycling of the rounds in the rifle. Once again from what I've read and comprehended, the dwell time for a middy is optimal for cycling the rifle. Peep on the link below. I read a more in depth article, but could not find it at first glance. Check the AR Discussion FAQ forum. As usual, if I have misinformed please let me know. I always like to learn more!

http://www.ar15.com/content/page.html?id=256
DM1975  [Team Member]
8/23/2011 10:50:18 AM
Hype...

I finally bought one of these mid length gas systems to see what it is all about and I don't see much of a difference at all. As far as dwell time, my carbine length gas system rifles work flawlessly, from 10.5" up to 14.5" barrels with not a single issue. I am in no way saying that the mid length gas system is junk, I just do not see a real difference with mine at all. Accuracy difference due to sight length? Again, I do not see much effect either way. Going from shooing the M16A2 and A4 to shooting the M4 I didn't notice that much of a difference at all, so I am sure sticking the front sight in the middle wont effect it much either. This is just me though, as I am sure for others it greatly improves accuracy, dwell time, does the dishes, and swallows every time as well.

Disclaimer: My mind may change with the more I use a mid length as I am not infallible.
beprepared  [Member]
8/23/2011 11:10:37 AM
- Mod delete. This is not GD. -
albatrossarmament  [Member]
8/23/2011 11:16:06 AM
- Mod delete. This is not GD. -
Barnacle_Bill  [Member]
8/23/2011 11:31:12 AM
Another consideration is that a 20" with a rifle gas system, a 16" with a middy gas system and a 14.5" with a carbine gas system all put the bayonet lug the same distance behind the flash suppressor, that distance being correct to mount a standard military bayonet (M7, M9 or USMC OKC-3S ). On a 16" with a carbine gas system, the distance between the flash suppressor and bayonet lug is 1.5" longer and the ring on the bayonet would end up flopping around loose on the barrel behind the flash suppressor, instead of on the flash suppressor where it is designed to fit. This only matters if you care about fixing a bayonet, of course. I hear the Marines actually use them in the sand box, but it probably won't come up much for anybody else anyplace else.
DM1975  [Team Member]
8/23/2011 12:09:54 PM
Originally Posted By Barnacle_Bill:
Another consideration is that a 20" with a rifle gas system, a 16" with a middy gas system and a 14.5" with a carbine gas system all put the bayonet lug the same distance behind the flash suppressor, that distance being correct to mount a standard military bayonet (M7, M9 or USMC OKC-3S ). On a 16" with a carbine gas system, the distance between the flash suppressor and bayonet lug is 1.5" longer and the ring on the bayonet would end up flopping around loose on the barrel behind the flash suppressor, instead of on the flash suppressor where it is designed to fit. This only matters if you care about fixing a bayonet, of course. I hear the Marines actually use them in the sand box, but it probably won't come up much for anybody else anyplace else.


I didn't even carry a bayonet in Iraq, but they are nice to have when you need them, no doubt on that.
apierce918  [Member]
8/23/2011 1:12:59 PM
Originally Posted By DM1975:
Hype...

I finally bought one of these mid length gas systems to see what it is all about and I don't see much of a difference at all. As far as dwell time, my carbine length gas system rifles work flawlessly, from 10.5" up to 14.5" barrels with not a single issue. I am in no way saying that the mid length gas system is junk, I just do not see a real difference with mine at all. Accuracy difference due to sight length? Again, I do not see much effect either way. Going from shooing the M16A2 and A4 to shooting the M4 I didn't notice that much of a difference at all, so I am sure sticking the front sight in the middle wont effect it much either. This is just me though, as I am sure for others it greatly improves accuracy, dwell time, does the dishes, and swallows every time as well.

Disclaimer: My mind may change with the more I use a mid length as I am not infallible.


It won't affect the inherent accuracy, I think he just meant to say its easier to be more accurate with a longer sight radius.
occasionalvisitor  [Member]
8/23/2011 1:41:11 PM
There are two types of mid-length, and there appears to be a lot of confusion about what mid-length means.

#1 There are mid-length (longer) handguards used with standard length carbine gas systems. The standard front sight post is cut down (gas system still used), and a 2nd FSB is attached closer to the muzzle (gas system not active) to use the sight post, OR a front sight is attached a mid-length quad rail. The advantage here can be a longer sight radius which can can it easier to shoot more accurately, a long with longer handguards which make is easier to stabilize the rifle.

#2 There are mid-length gas systems. The gas port drilled in the barrel is located closer to the muzzle of the barrel. Longer handguards and a longer gas tube are used (mid-length), and the FSB located closer to the muzzle of the barrel to align with the relocated gas port. Mid-gas barrels are supposed to shoot softer than carbine gas barrels, and are supposed to have fewer ejection and extraction problems.
hellbound  [Team Member]
8/23/2011 1:47:53 PM
Originally Posted By occasionalvisitor:
There are two types of mid-length, and there appears to be a lot of confusion about what mid-length means.

#1 There are mid-length (longer) handguards used with standard length carbine gas systems. The standard front sight post is cut down (gas system still used), and a 2nd FSB is attached closer to the muzzle (gas system not active) to use the sight post, OR a front sight is attached a mid-length quad rail. The advantage here can be a longer sight radius which can can it easier to shoot more accurately, a long with longer handguards which make is easier to stabilize the rifle.

#2 There are mid-length gas systems. The gas port drilled in the barrel is located closer to the muzzle of the barrel. Longer handguards and a longer gas tube are used (mid-length), and the FSB located closer to the muzzle of the barrel to align with the relocated gas port. Mid-gas barrels are supposed to shoot softer than carbine gas barrels, and are supposed to have fewer ejection and extraction problems.


#1 is incorrect. what you described is a "dissipator" and not a midlength.

midlength refers to #2. the longer sight radius is a side effect of using a longer gas system. the only person confused it seems is you...
Barnacle_Bill  [Member]
8/23/2011 1:49:47 PM
Originally Posted By DM1975:
I didn't even carry a bayonet in Iraq, but they are nice to have when you need them, no doubt on that.


If you trust Wikipedia, their article on bayonets lists several occasions from the Falklands through Iraq & Afganistan where the Brits made bayonet charges. An article I found elsewhere on one of the incidents from Iraq included the following quote:

“I wanted to put the fear of God into the enemy. I could see some dead bodies and eight blokes, some scrambling for their weapons. I’ve never seen such a look of fear in anyone’s eyes before. I’m over six feet; I was covered in sweat, angry, red in the face, charging in with a bayonet and screaming my head off. You would be scared, too.”

Corporal Brian Wood
Princess of Wales’s Royal Regiment


sinlessorrow  [Team Member]
8/23/2011 2:11:20 PM
Originally Posted By Barnacle_Bill:
Originally Posted By DM1975:
I didn't even carry a bayonet in Iraq, but they are nice to have when you need them, no doubt on that.


If you trust Wikipedia, their article on bayonets lists several occasions from the Falklands through Iraq & Afganistan where the Brits made bayonet charges. An article I found elsewhere on one of the incidents from Iraq included the following quote:

“I wanted to put the fear of God into the enemy. I could see some dead bodies and eight blokes, some scrambling for their weapons. I’ve never seen such a look of fear in anyone’s eyes before. I’m over six feet; I was covered in sweat, angry, red in the face, charging in with a bayonet and screaming my head off. You would be scared, too.”

Corporal Brian Wood
Princess of Wales’s Royal Regiment




ive actually head about that before, apparently they are really scared of knives for some reason
BoovarBjarki  [Member]
8/23/2011 2:38:21 PM
I have a 14.5" mid and carbine length. They both get equally as dirty and hot. The longer sight on the mid makes it easier for a beginner to get on target and the mid also has a smoother felt recoil. Other than that they are pretty much the same.
beprepared  [Member]
8/23/2011 2:45:09 PM
Originally Posted By hellbound:
Originally Posted By occasionalvisitor:
There are two types of mid-length, and there appears to be a lot of confusion about what mid-length means.

#1 There are mid-length (longer) handguards used with standard length carbine gas systems. The standard front sight post is cut down (gas system still used), and a 2nd FSB is attached closer to the muzzle (gas system not active) to use the sight post, OR a front sight is attached a mid-length quad rail. The advantage here can be a longer sight radius which can can it easier to shoot more accurately, a long with longer handguards which make is easier to stabilize the rifle.

#2 There are mid-length gas systems. The gas port drilled in the barrel is located closer to the muzzle of the barrel. Longer handguards and a longer gas tube are used (mid-length), and the FSB located closer to the muzzle of the barrel to align with the relocated gas port. Mid-gas barrels are supposed to shoot softer than carbine gas barrels, and are supposed to have fewer ejection and extraction problems.


#1 is incorrect. what you described is a "dissipator" and not a midlength.

midlength refers to #2. the longer sight radius is a side effect of using a longer gas system. the only person confused it seems is you...


Wait now I am confused...I thought a dissy is a 16" barrel with a rifle length handguard. It can use either a carbine or middy gas system. The FSB is obviously closer to the muzzle b/c of the rifle length handguard (12") on the 16" barrel.

Hence the name dissipator, the heat from the barrel has more area to "dissipate"? Yeah that was a question. Learn me something new...

hellbound  [Team Member]
8/23/2011 2:56:49 PM
Originally Posted By beprepared:
Originally Posted By hellbound:
Originally Posted By occasionalvisitor:
There are two types of mid-length, and there appears to be a lot of confusion about what mid-length means.

#1 There are mid-length (longer) handguards used with standard length carbine gas systems. The standard front sight post is cut down (gas system still used), and a 2nd FSB is attached closer to the muzzle (gas system not active) to use the sight post, OR a front sight is attached a mid-length quad rail. The advantage here can be a longer sight radius which can can it easier to shoot more accurately, a long with longer handguards which make is easier to stabilize the rifle.

#2 There are mid-length gas systems. The gas port drilled in the barrel is located closer to the muzzle of the barrel. Longer handguards and a longer gas tube are used (mid-length), and the FSB located closer to the muzzle of the barrel to align with the relocated gas port. Mid-gas barrels are supposed to shoot softer than carbine gas barrels, and are supposed to have fewer ejection and extraction problems.


#1 is incorrect. what you described is a "dissipator" and not a midlength.

midlength refers to #2. the longer sight radius is a side effect of using a longer gas system. the only person confused it seems is you...


Wait now I am confused...I thought a dissy is a 16" barrel with a rifle length handguard. It can use either a carbine or middy gas system. The FSB is obviously closer to the muzzle b/c of the rifle length handguard (12") on the 16" barrel.

Hence the name dissipator, the heat from the barrel has more area to "dissipate"? Yeah that was a question. Learn me something new...



that was the bushmaster version, i've seen a number of variants of the "dissipator", all of which are comprised of a non functioning FSB, and a low profile gas block... don't get confused, there is no need to be. just know that RIFLE, MIDLENGTH, INTERMEDIATE, and CARBINE all refer to the gas system of the AR15 platform.

either way, the term midlength refers to the GAS SYSTEM. midlength handguards are named such as they are designed to work with that gas system. having a longer handguard does not make a carbine a midlength, you're just using a longer HG on a carbine.

i have 2 14.5" middys with 12" (rifle or full length) rails, they aren't "rifles"
beprepared  [Member]
8/23/2011 2:59:54 PM
Thanks!
Direct-Drive  [Member]
8/23/2011 3:08:11 PM
Originally Posted By hellbound:
Originally Posted By beprepared:
Originally Posted By hellbound:
Originally Posted By occasionalvisitor:
There are two types of mid-length, and there appears to be a lot of confusion about what mid-length means.

#1 There are mid-length (longer) handguards used with standard length carbine gas systems. The standard front sight post is cut down (gas system still used), and a 2nd FSB is attached closer to the muzzle (gas system not active) to use the sight post, OR a front sight is attached a mid-length quad rail. The advantage here can be a longer sight radius which can can it easier to shoot more accurately, a long with longer handguards which make is easier to stabilize the rifle.

#2 There are mid-length gas systems. The gas port drilled in the barrel is located closer to the muzzle of the barrel. Longer handguards and a longer gas tube are used (mid-length), and the FSB located closer to the muzzle of the barrel to align with the relocated gas port. Mid-gas barrels are supposed to shoot softer than carbine gas barrels, and are supposed to have fewer ejection and extraction problems.


#1 is incorrect. what you described is a "dissipator" and not a midlength.

midlength refers to #2. the longer sight radius is a side effect of using a longer gas system. the only person confused it seems is you...


Wait now I am confused...I thought a dissy is a 16" barrel with a rifle length handguard. It can use either a carbine or middy gas system. The FSB is obviously closer to the muzzle b/c of the rifle length handguard (12") on the 16" barrel.

Hence the name dissipator, the heat from the barrel has more area to "dissipate"? Yeah that was a question. Learn me something new...



that was the bushmaster version, i've seen a number of variants of the "dissipator", all of which are comprised of a non functioning FSB, and a low profile gas block... don't get confused, there is no need to be. just know that RIFLE, MIDLENGTH, INTERMEDIATE, and CARBINE all refer to the gas system of the AR15 platform.

either way, the term midlength refers to the GAS SYSTEM. midlength handguards are named such as they are designed to work with that gas system. having a longer handguard does not make a carbine a midlength, you're just using a longer HG on a carbine.

i have 2 14.5" middys with 12" (rifle or full length) rails, they aren't "rifles"

This.

A 16" with mid-gas is in proper scale.


beprepared  [Member]
8/23/2011 3:24:27 PM
Originally Posted By hellbound:
Originally Posted By beprepared:
Originally Posted By hellbound:
Originally Posted By occasionalvisitor:
There are two types of mid-length, and there appears to be a lot of confusion about what mid-length means.

#1 There are mid-length (longer) handguards used with standard length carbine gas systems. The standard front sight post is cut down (gas system still used), and a 2nd FSB is attached closer to the muzzle (gas system not active) to use the sight post, OR a front sight is attached a mid-length quad rail. The advantage here can be a longer sight radius which can can it easier to shoot more accurately, a long with longer handguards which make is easier to stabilize the rifle.

#2 There are mid-length gas systems. The gas port drilled in the barrel is located closer to the muzzle of the barrel. Longer handguards and a longer gas tube are used (mid-length), and the FSB located closer to the muzzle of the barrel to align with the relocated gas port. Mid-gas barrels are supposed to shoot softer than carbine gas barrels, and are supposed to have fewer ejection and extraction problems.


#1 is incorrect. what you described is a "dissipator" and not a midlength.

midlength refers to #2. the longer sight radius is a side effect of using a longer gas system. the only person confused it seems is you...


Wait now I am confused...I thought a dissy is a 16" barrel with a rifle length handguard. It can use either a carbine or middy gas system. The FSB is obviously closer to the muzzle b/c of the rifle length handguard (12") on the 16" barrel.

Hence the name dissipator, the heat from the barrel has more area to "dissipate"? Yeah that was a question. Learn me something new...



that was the bushmaster version, i've seen a number of variants of the "dissipator", all of which are comprised of a non functioning FSB, and a low profile gas block... don't get confused, there is no need to be. just know that RIFLE, MIDLENGTH, INTERMEDIATE, and CARBINE all refer to the gas system of the AR15 platform.

either way, the term midlength refers to the GAS SYSTEM. midlength handguards are named such as they are designed to work with that gas system. having a longer handguard does not make a carbine a midlength, you're just using a longer HG on a carbine.

i have 2 14.5" middys with 12" (rifle or full length) rails, they aren't "rifles"


So a dissipator has nothing to do with the gas system, just the fact that it has a rifle length handguard on a specific gas system? Also the non-functioning FSB and low-profile gas block. So essentially your dissipator can be a middy or carbine. Can a dissipator have a rifle length gas system or would that defeat the purpose?
Desert_AIP  [Team Member]
8/23/2011 3:48:04 PM
Originally Posted By Scvette01:
So the FSB is further forward then the M4?
What does that do for it


Other way around.

M4 uses a carbine length gas system. The Midlength gas system is 2" longer.
hellbound  [Team Member]
8/23/2011 3:59:42 PM
Originally Posted By beprepared:
So a dissipator has nothing to do with the gas system, just the fact that it has a rifle length handguard on a specific gas system? Also the non-functioning FSB and low-profile gas block. So essentially your dissipator can be a middy or carbine. Can a dissipator have a rifle length gas system or would that defeat the purpose?


good luck trying to get your 16" barrel to run on a rifle gas system with a carbine stock setup.

i'm sure it could be done, low profile rifle gas on a 16" barrel, covered with a 13-14" rail. but you'd probably run out of space on the barrel, or cut it VERY close (depending on the make of the rail), when you go to mount the standard FSB.

personally, i think the dissipator is an outdated configuration. it was from a time when free float rails, folding BUIS, optics, and low profile gas blocks weren't the norm. It was bushmaster's way of using existing parts to build something "better". Today, I'd sooner run a free float handguard, over any gas system i want, and use a troy folding front sight. longer gas system, longer sight radius, less cluttered sight picture, less weight = better balance.