Mid Length 16" AR vs. Carbine Length

[Abraham]

I know in the AR world, it's all the rage to prefer a "Mid Length" gas system.

My Colt LE6920 is Carbine Length i.e. shorter. That said, if it's not as efficient or whatever compared to the M.L., the troops seem to do just fine with it. So what do I not know about the two gas systems that would me say "Eureka", I see the light!

The only think I've heard that makes a M.L. preferable is a slightly less recoil and that it's a bit more technically efficient? I confess, if my C.L. gas system works just fine, is it necessary to tweak it for a wee bit more efficiency I don't really need?

So, if I'm completely off track, school me please.

Or, is a Mid Length gas system a marketing ploy that many have bought into...?

And people like to be snobs, irrespective of subject matter...

Yes Jeeves, bring me the Château Margot 1947 and not that dreadful 1948, oh dearie me...

[Dadtodabone]

It's all about balance. Carbine length systems will eventually wear out your moving parts in a LE6920 in a shorter time period than a mid length system. If you utilize a suppressor the gas pressure cab be extreme and blow back through the chamber.
The way I understand it, mil-spec carbines utilize a 7 inch long gas system. Which is good for barrels up to 14.5 inches long. You want the gas port to be at the halfway mark on the barrel to optimize dwell time and gas pressure. Increasing barrel length to 16 inches, due to the NFA minimum barrel length, increases dwell time and increases pressure as the bullet remains in the barrel for a longer period after passing the gas port. The gas pressure 7 inches out from the chamber is about twice that of the pressure at 9 inches, and of longer duration as the bullet travels the extra inches.
So a mid length system at 9 inches would produce enough pressure to cycle the action reliably, but with softer, less damaging pulse.
That said I have about 8k rounds through my oldest LE6920 with no measurable wear in the chamber or barrel and zero broken parts in the bolt or buffer. It is still capable of producing <1" groups at 100 yards with Black Hills 77grn OTM ammo. I don't run it suppressed and keep it clean and lubricated.

[cajunautoxer]

Not a ploy midlength is better. I have a Voodoo 16.5 inch with rifle length gas system. I havn't had a chance to put it together. I'm gonna go with JP low mass BCG and adjustable gas block

[The Annoyed Man]

I built my recent DMR build (18" heavy 1:8 Wylde barrel) with a rifle length gas system. What I notice in terms of the shooting experience is a somewhat more dampened recoil impulse. Not that ARs recoil that hard anyway, but it isn't so much "less" as it is "smoother" and less sharp.

I have heard, but have no idea if it is true or not, that the increased dwell time of the gas impulse also gives time for the gas temperature to drop a bit, which contributes to making things easier on the receiver internals. They say that rifle length systems consequently extend the life of the parts. It makes sense, but I don't know if there is any hard data to support that. But, it does make for a somewhat more pleasant shooting experience. The difference isn't DRAMATIC, but it is there.

[gljjt]

How can you tell what you have? Measure from chamber to gas port?

[Abraham]

Thanks all for the education.

I've a neighbor who shoots a Rock River AR and he and I traded off one day. At the time, I thought his rifle had a softer recoil, but I reconsidered and thought, nah, can't be. They're both 16" rifles shooting the same ammo. Little did I know...

Now, with my newly acquired information, I'm going to confirm if his is a M.L. From what I just learned (thanks again) my guess is yes, it's a M.L.

I also wonder if I can swap out my C.L. for a M.L. on one of my LE6920's (why - curiosity of course)

I've no clue how to go about doing it or how much it would cost or if such an idea is feasible?

Perhaps, the simplest thing to do (and for all I know is the most cost effective) is just buy a 16" BCM that already comes with a M.L. and be done with it.

Of course, I told my wife I was only going to buy one AR and now I've got two, with three I can probably get a divorce thrown in the mix...not really, at worst she'll make an ugly face, walk away shaking her head and muttering.

[CleverNickname]

My Colt LE6920 is Carbine Length i.e. shorter. That said, if it's not as efficient or whatever compared to the M.L., the troops seem to do just fine with it.

"The troops" are using either a 20" rifle or a 14.5" carbine. Nobody's using a 16" barrel in the military. For what it's worth, the carbine-length system was originally designed for use in the CAR-15 and is still longer than optimal for even the M4's 14.5" barrel.

That said, yes a carbine-gassed 16" gun isn't optimal but unless it really bothers you for some reason just go shoot it.

[The Annoyed Man]

I also wonder if I can swap out my C.L. for a M.L. on one of my LE6920's (why - curiosity of course)

I've no clue how to go about doing it or how much it would cost or if such an idea is feasible?

Perhaps, the simplest thing to do (and for all I know is the most cost effective) is just buy a 16" BCM that already comes with a M.L. and be done with it.

Swapping out the barrel is the ONLY way to do it because of the pre-drilled position of the gas port in the barrel. If you tried to put a ML system on a CL drilled barrel, you'd be venting gas out the top of the barrel, but it would just be escaping without being put to work.....because the gas block would be forward of the hole.

[The Annoyed Man]

How can you tell what you have? Measure from chamber to gas port?

If you have a carbine length barrel, unless you paid a slight premium for a ML gas system and it said on the packaging somewhere that you had a ML system, then you have about a 99.9% certainty of it being a carbine length gas system. You kind of have to go out of your way to get a longer than normal gas system for your barrel length. So.... If you have a 16" barrel, you most likely have a carbine length system. If you have an 18" barrel, you most likely have a mid-length system. And if you have a 20" or longer barrel, you most likely have a rifle length gas system. A mid-length system on a 16" barrel would fall under "custom features".

The fact that my 18" DMR barrel has a rifle length gas system is part of what makes it a "custom" barrel. (....the Wylde chamber, 1:8 twist, and stainless steel being the other "custom" features....)

[Abraham]

TAM,

Thanks!

Looks like a new M.L. AR may be in my future.

CN,

"Nobody's using a 16" barrel in the military."

Oh, O.K., thanks - Learn something new every day.

In the Army, I trained with an M-14 many moons ago and to this day I couldn't tell you the barrel length.

As for: "That said, yes a carbine-gassed 16" gun isn't optimal but unless it really bothers you for some reason just go shoot it."

Hhhmmm, just recently I was correctly reminded this site is for gun enthusiasts. "Just go shoot it" doesn't seem to convey that spirit...

[gljjt]

How can you tell what you have? Measure from chamber to gas port?

If you have a carbine length barrel, unless you paid a slight premium for a ML gas system and it said on the packaging somewhere that you had a ML system, then you have about a 99.9% certainty of it being a carbine length gas system. You kind of have to go out of your way to get a longer than normal gas system for your barrel length. So.... If you have a 16" barrel, you most likely have a carbine length system. If you have an 18" barrel, you most likely have a mid-length system. And if you have a 20" or longer barrel, you most likely have a rifle length gas system. A mid-length system on a 16" barrel would fall under "custom features".

The fact that my 18" DMR barrel has a rifle length gas system is part of what makes it a "custom" barrel. (....the Wylde chamber, 1:8 twist, and stainless steel being the other "custom" features....)

Thanks! Mine are out of the box 16" Bushmaster and DPMS (I know, not Colt/LaRue/etc., but they are fine for weekend plinking) so it sounds like I have Carbine length systems.

[The Annoyed Man]

In the Army, I trained with an M-14 many moons ago and to this day I couldn't tell you the barrel length.

22"

[The Annoyed Man]

Thanks! Mine are out of the box 16" Bushmaster and DPMS (I know, not Colt/LaRue/etc., but they are fine for weekend plinking) so it sounds like I have Carbine length systems.

You're welcome. Honestly, I wouldn't worry about it too much. My first AR was a Bushmaster 24" Varminter. My second one was a home-built M4 carbine, primarily from DPMS parts. They were both just fine and functioned perfectly reliably. Over the years I've gotten more interested in having upgraded custom AR's, and as it happens, most upgraded parts are made to mil-spec, so mine are now mil-spec rifles. But back when they weren't, I never had any issues with them, and I would have been perfectly comfortable with them in almost any scenario that I would be likely to find myself in.

I have seen members here reply to me that they would never trust their lives to an AR that wasn't mil-spec. Well, I can see where they are coming from, but this isn't "the stans" .....yet..... and I'm hopeful that the ballot box will remedy things before the bullet box becomes necessary, and at 62 years old (today, by the way), I'm not headed off to war.

[CleverNickname]

CN,

"Nobody's using a 16" barrel in the military."

Oh, O.K., thanks - Learn something new every day.

In the Army, I trained with an M-14 many moons ago and to this day I couldn't tell you the barrel length.

As for: "That said, yes a carbine-gassed 16" gun isn't optimal but unless it really bothers you for some reason just go shoot it."

Hhhmmm, just recently I was correctly reminded this site is for gun enthusiasts. "Just go shoot it" doesn't seem to convey that spirit...

Heh, I saw your post on M4C.

My point is that if you have a carbine-gassed AR with a 16" barrel, I don't think it's worth the trouble to sell it and go buy a new one, just for that reason. But if you didn't have an AR and were looking to buy, then having a carbine-gassed 16" upper would be a knock against a particular gun. But I'd still rather have a Colt than a DPMS midlength, for example, because the Colt's better in other areas.

[Abraham]

CN,

"My point is that if you have a carbine-gassed AR with a 16" barrel, I don't think it's worth the trouble to sell it and go buy a new one, just for that reason."

We agree.

I have no intention of selling my current AR's. Never did.

I would simply add to my collection a 16" M.L. AR like a BCM or some other high quality mfg. 16" M.L. AR.

I'd go the 14.5" route, but I'm not interested in all the paperwork and bother to own one.

Additionally, I might also buy a 20" R.L. gas system AR to add to my collection. I've got AR fever, I guess...

Plus, I'm looking into buying a Ruger Scout Bolt Action, just haven't decided in what caliber yet.