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Posted: 5/19/2008 3:20:54 PM EDT
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Pardon my ignorance, but what defines an AR-15 as midlength? I see all these middy threads. |
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Gas tube length. Midlength gas systems can be used on any length of barrel, with 14.5 usually being the shortest. A vast majority of midlength gas systems are usually found on 16" barrels, so a "midlength" AR is usually a 16" barreled AR with a midlength gas system. |
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A carbine and a midlength may both have 16" barrels. But the mid length's handguard is longer, the front sight base, which contains the gas port, is closer to the muzzle than with a carbine. The M16 Carbine used to have an 11.5" barrel with a long flash hider/suppressor. Since most civilian AR-15's must, due to NFA, have 16" barrels, it is possible to move the front sight base farther out, pick the gas off a more distant point on the barrel, with a longer gas tube and lower pressure. Now the rifle works with a lower pressure, longer gas pulse. |
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A carbine and a midlength may both have 16" barrels. But the mid length's handguard is longer, the front sight base, which contains the gas port, is closer to the muzzle than with a carbine. The M16 Carbine used to have an 11.5" barrel with a long flash hider/suppressor. Since most civilian AR-15's must, due to NFA, have 16" barrels, it is possible to move the front sight base farther out, pick the gas off a more distant point on the barrel, with a longer gas tube and lower pressure. Now the rifle works with a lower pressure, longer gas pulse. |
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So whats the length of the gas system to determine if its a mid-length? Is a standard M4 barrel configuration and gas system mid-length? A 14.5 inch barrel with a middy system would have to push the gas block really close to the muzzle correct. I take it my Noveske wouldnt be considered a middy as the gas system length is no longer than any of my other carbine length rifles? Right?  |
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Standard Carbine Gas System -- Gas port is located ~7.5" from the back of the barrel. Mid-Length Gas System -- Gas port is located ~9.5" from the back of the barrel. Rifle Length Gas System -- Gas port is located ~13.0" from the back of the barrel. |
Sabre Defence with 14.5" barrel midlength gas system. My Build on Mega Receivers 16" barrel midlength gas system.   |
So for you and me, here in the land of the big PX, who only have to worry about whether we can afford enough rounds to stay proficient, a midlength carbine is probably a better choice than a carbine-length carbine. But the Army standardized the M4 with its carbine-length gas system for their own reasons, and paper punching was not among them. |
The rifle length gas system on a 18" barrel has the same problems yet the Mk12 soldiers on. The problem is the dwell time might not be enough to cycle the weapon under cold conditions or when using wimpy ammo(considering the .mil uses 5.56 loads that should not be an issue). However that problem is resolved by drilling out a larger gas port. The problem is that the military already has the logistics in place and large fleet of M4's already in service. Colt Canada formerly known as Diamaco produces a midlegnth gas systems for the Canadian SF. Also many companies are starting to "see the light" for their 'hard use' weapons like Noveske and KAC producing midlength systems. |
 Denny's Guns-Global Tactical Operator midlength gas system 16" barrel on Colt 6721 A3 tactical carbine which I installed myself. No one said it yet but the technical answer to the midlength gas system is the gas port are more forward than the carbine gas port by exactly 2.000" per previous thread discussions as said by several member gunsmiths here. I've got all three midlength, carbine and 20" rifle gas systems and my favorite is the midlength because of the reasons said by the other members, smoother action, longer sight radius, longer handguard for more room for accessories such as lights and vertical grips, better reliability, and standard bayonets could be used (unlike a 16" carbine gas system which would need a bayonet lug more forward of the FSB or a special bayonet with longer handles). Also with the midlength extra strength extractor spring and heavier buffer are not required which the carbine gas system requires for better reliability. Other manufacturers that are selling the midlength carbines are Armalite, LMT (MRP model), RRA, Sabre Defence, etc. Here's good technical info on the rifle, midlength and carbine gas systems. How it Works - The AR Gas Operation and How Everything Works in Harmony - tacked thread link |
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