Okay I know this has been answered but I can't find it.

The RRA arms site doesn't say "mid length upper" it lists "mid length handguard" as an option on some uppers.  Does this mean that it has a mid length gas system also?

Armalite doesn't list it either, but it looks like all the carbine uppers are midlength.  Is this the case?

Are there any advantages to midlength uppers beside the looks and the bayonet working?   I seem to recall someone saying it was better on the bolt/carrier because of the longer gas system.  Anything else?

Are all midlengths heavy bbls?

I'm going to start a new build and I'm thinking of a mid length, this would become my primary AR with my Busmaster set aside for my son.

Quoted: Okay I know this has been answered but I can't find it. The RRA arms site doesn't say "mid length upper" it lists "mid length handguard" as an option on some uppers.  Does this mean that it has a mid length gas system also? RRA lists a "Carbine" as anything not using a rifle length gas system.  Just look at the pics on the website and you can tell if you are getting a midlength or a carbine length. Armalite doesn't list it either, but it looks like all the carbine uppers are midlength.  Is this the case? See above. Are there any advantages to midlength uppers beside the looks and the bayonet working?   I seem to recall someone saying it was better on the bolt/carrier because of the longer gas system.  Anything else? Increased sight radius over a carbine length.  Otherwise you named most of the benefits. Are all midlengths heavy bbls? No, but most RRA midlength and ArmaLite midlengths are heavy profile.  It is cheaper for the manufacturers to do heavier profiles than it is to do lighter profiles.  If you want a light profile, send the upper to ADCO to have it turned down to the diameter you want. I'm going to start a new build and I'm thinking of a mid length, this would become my primary AR with my Busmaster set aside for my son.

search for "midlength" and you will find plenty of answers.  

currahee, I have been researching the same issue.  Even posted a similiar question a few days ago. For whatever its worth, here is what I have concluded from my research.  Research which included calling the different manufacturers technical departments, going to the different dealers in the area, as well as this forum which I am sure is full of knowledgeable people as well as those who are biased toward one style or another.

The length of the gas system is just part of the equation.  Barrel length twist and weight of bullet also play a factor.
The carbine version, M4, does have slightly higher pressures than a mid-length but not enough to make a bit of difference in the life  or function of your gun.   The carbines have been around for years now and is a proven durable rifle. Every manufacturer, except Armalite, makes them and do not feel there is an inherent problem with the design.  One huge dealer close to me, Kieslers, doesn't even stock mid-lengths of the manufacturers they carry.  Says he can get it but doesn't ever have anyone ask for them. At least not enough to stock them.  

On the other hand, Armalite, thinks a mid-length is the only way to go and they don't make M4 style rifles.  They published a recent article you should be able to find on the web.

I think the mid-length probably beats the carbine by a nose hair in the overall picture because you can add more stuff to it, and better sight aperture but i am not letting the question of reliability or durability be a factor in my choice.   I like the M4 for its looks and resale, if times ever get tough.

Quoted: currahee, I have been researching the same issue.  Even posted a similiar question a few days ago. For whatever its worth, here is what I have concluded from my research.  Research which included calling the different manufacturers technical departments, going to the different dealers in the area, as well as this forum which I am sure is full of knowledgeable people as well as those who are biased toward one style or another. The length of the gas system is just part of the equation.  Barrel length twist and weight of bullet also play a factor. The carbine version, M4, does have slightly higher pressures than a mid-length but not enough to make a bit of difference in the life  or function of your gun.   The carbines have been around for years now and is a proven durable rifle. Every manufacturer, except Armalite, makes them and do not feel there is an inherent problem with the design.  One huge dealer close to me, Kieslers, doesn't even stock mid-lengths of the manufacturers they carry.  Says he can get it but doesn't ever have anyone ask for them. At least not enough to stock them.   On the other hand, Armalite, thinks a mid-length is the only way to go and they don't make M4 style rifles.  They published a recent article you should be able to find on the web. I think the mid-length probably beats the carbine by a nose hair in the overall picture because you can add more stuff to it, and better sight aperture but i am not letting the question of reliability or durability be a factor in my choice.   I like the M4 for its looks and resale, if times ever get tough.

Red-  What are you talking about?  Midlength always refers to the length of the gas system.  When a rifle has a Carbine gas system, it has exactly that- a carbine length gas system whether you might consider it a true carbine or not.  Some carbines use midlength gas systems but are called midlengths to clarify the gas system used.  Rifles using midlength gas systems can have barrels of the same length, twist, etc.  He never asked about bullet weight and twists.  

Blue- your wording is unclear- you consider the carbine version of the AR15 to be the M4?  That's wrong.  An M4 is considered a carbine and uses a carbine length gas system.  You are 100% wrong when you say that the higher operating pressures of the carbine do not make a difference in the longevity of the internal parts.  I don't think anyone has raced a carbine and a midlength to death but it pretty much goes without saying- higher operating pressures put more stress on internals- period.  

Green-  There may not be an inherent problem, but it's been proven that Midlength Gas Systems are easier on the internals.  The impulse of the recoil is less which translates to less stress on the internals.

Why do you say you can "add more stuff" to a midlength?  What "Stuff" are you talking about and how do you mean more?  Is is possible to add "more" bipod?  Midlengths do not have "better sight aperture"- they are almost always manufactured on flattops and the carry handles are what contain the sight apertures.  The sight apertures have been A2s for a long long time.  You mean Sight Radius and it's exactly 2" longer.  

M4s have better resale value?  

I wont ever buy another 16" barrel taht is not a mid length. Period. Its that much better.

Aside from the better gas system, you also get that much handguard to rest the rifle on. A 7.0 rail, FWIW, gets filled up fast.

Thanks for the replies.  I'm gonna order the lower after Christmas... it will take a while to get all of the parts but I definately plan on a mid length.

Quoted: The carbine version, M4, does have slightly higher pressures than a mid-length but not enough to make a bit of difference in the life  or function of your gun.

There is definitely a difference in the life and function of a carbine gas system vs. a midlength gas system. Whether or not that amounts to a practical difference depends a lot on the needs of the user. Here is the way this works though...

All of the components of the M16/AR15 system are designed with the original 20" rifle in mind. Pressure at the gas port is around 13k psi in a 20" system. Not only that but the gas has further to travel before it begins to unlock the bolt. These distances are important because we don't want the bolt to unlock until pressures in the barrel have dropped to a safe level.

In a carbine gas system, pressures are twice as high at the gas port (26k). Also, because of the higher pressure you see more gas port erosion (the gas erodes the gas port opening, making it bigger and funnelling even more gas into the system). Not only is the carbine operating at higher pressures, there is a shorter distance for the gas to travel to unlock the action. This can sometimes mean that the gun is trying to unlock and extract the brass before the pressure has dropped enough to allow the brass to shrink from the chamber walls.

Even when the carbine system works perfectly, it is cycling harder and faster than the rifle system. This means less time for the magazine to position the next round for the bolt to pick it up and load it. Marginal magazines that will run fine in a rifle, may not work in a carbine because they just can't position the round fast enough.

The midlength moves the gas port out, reducing gas pressure and cyclic rate. The reduced gas pressure means less wear an tear on the bolt over time (durability). The reduced cyclic rate means that you get better feeding (reliability).

Barring that though, here are a few immediate things that everyone shooting a midlength and carbine side by side will immediately notice:

1) Better sight radius
2) Smoother recoil impulse on the midlength
3) less exposed hot barrel to brand you with
4) That pigsticker you bought at the gun show only fits on the midlength

The carbines have been around for years now and is a proven durable rifle.

The carbine is unquestionably a fine rifle that will serve you just fine for tens of thousands of rounds. However, let's take a look at commonly sold items on AR15.com that were developed primarily to address the issues caused by the higher gas pressures in carbines:

1) extractor o-rings
2) enhanced extractor and ejector springs
3) heavy buffers
4) Extra strength magazine springs
5) Enhanced mag followers
6) Extra strength buffer springs
7) Improved bolts w/ redesigned extractors and lugs
8) Pigtail and fatboy gas tubes

thanks "bart"- you made my pissy arguing and rambling make a little more sense and helped me realize what I thought were smaller improvements are actually very big improvements in the midlength.

my new mid-length from dennysguns is far nicer than my bush M4gery in almost every way.  I'm sold.

Get a mid length and you'll never look at another 14.5" M4gery.

I'm sure it's nit picks and debatable, but good to see this info about the differences.

I am also shopping for a midlength, and the only reason i've been looking at M4 styles is because most of the midlengths are heavy profiles and i prefer a lighter barrel. I know I could have it turned down but that's a rather expensive option.

Quoted: I'm sure it's nit picks and debatable, but good to see this info about the differences. I am also shopping for a midlength, and the only reason i've been looking at M4 styles is because most of the midlengths are heavy profiles and i prefer a lighter barrel. I know I could have it turned down but that's a rather expensive option.

If you consider $64 an expensive option I suggest you find another hobby.

Turning down a mid-length to LW profile under the HGs shaves off 12 ounces.  It's worth it.

Does the turn down come as an option from RRA or Armalite? Or does it have to be sent off?

Quoted: Quoted: I'm sure it's nit picks and debatable, but good to see this info about the differences. I am also shopping for a midlength, and the only reason i've been looking at M4 styles is because most of the midlengths are heavy profiles and i prefer a lighter barrel. I know I could have it turned down but that's a rather expensive option. If you consider $64 an expensive option I suggest you find another hobby.h

$64 + $50 for the dissassembly for me would be $114, as I would be buying a complete upper. Then you have to factor in insured shipping.  I may just get a RRA mid and have it turned down later. I wish Stag made a mid.

Quoted: Does the turn down come as an option from RRA or Armalite? Or does it have to be sent off?

ALL Rock River guns have heavy barrels under the handguards, even the M4 types, I had this confirmed by a rep here:

ar15.com/forums/topic.html?b=2&f=38&t=148987&page=1

Don't know about Armalite.

Quoted: Quoted: Quoted: I'm sure it's nit picks and debatable, but good to see this info about the differences. I am also shopping for a midlength, and the only reason i've been looking at M4 styles is because most of the midlengths are heavy profiles and i prefer a lighter barrel. I know I could have it turned down but that's a rather expensive option. If you consider $64 an expensive option I suggest you find another hobby. Turning down a mid-length to LW profile under the HGs shaves off 12 ounces.  It's worth it. $64 + $50 for the dissassembly for me would be $114, as I would be buying a complete upper. Then you have to factor in insured shipping.  I may just get a RRA mid and have it turned down later. I wish Stag made a mid.

I ordered the upper from ADCO and specified the turned down option at that time.  They did not charge the disassembly fee and only added the labor for the profilng, which was $60 back then.  I thought the $50 was applied if the customer sent in an assembled upper.  Check with Steve to make sure this has not changed.

Shipping was, and still is, $4.

If you check with Steve and this has changed, or I am plain wrong, then please post a correction.

Quoted: I ordered the upper from ADCO and specified the turned down option at that time.  They did not charge the disassembly fee and only added the labor for the profilng, which was $60 back then.  I thought the $50 was applied if the customer sent in an assembled upper.  Check with Steve to make sure this has not changed. Shipping was, and still is, $4. If you check with Steve and this has changed, or I am plain wrong, then please post a correction.

Thanks for the tip, i'll keep them in mind when shopping then for that very reason.

I've never really enjoyed shooting the carbines, especially the 14.5 + permanent whatevers.  I really like shooting the midlengths.  I notice that much of a difference in how it feels shooting it.

+1 on the middys!

...for the record Armalite makes the SOF carbine in .223 and .308...

Armalite seems to be all HBAR too.  So it comes down to either an Armalite and having it turned down or ordering a RR from ADCO allready turned down.  

I've got to check on prices as I have an Armalite dealer local.

Quoted: Armalite seems to be all HBAR too.  So it comes down to either an Armalite and having it turned down or ordering a RR from ADCO allready turned down.

Sabre Defence and CMMG both offer mid-length uppers with government profile barrels.

Quoted: Quoted: Armalite seems to be all HBAR too.  So it comes down to either an Armalite and having it turned down or ordering a RR from ADCO allready turned down.   Sabre Defence and CMMG both offer mid-length uppers with government profile barrels.

Also keep an eye on Bravo Company USA, they will have some excellent quality Govt. profile 16", mid-length barrels very soon.

Quoted: Quoted: Sabre Defence and CMMG both offer mid-length uppers with government profile barrels. Also keep an eye on Bravo Company USA, they will have some excellent quality Govt. profile 16", mid-length barrels very soon.

I didn't know there were so many options, this has been a productive thread.

I bought CMMG Mid-Length uppers w/Govt. profile barrels.   Then I contacted Grant at G&R and

got the CMT M16 bolt carriers w/MP inspected bolts from him.  You might also want to use a Gas-

Buster CH in place of the stock one. For a little extra insurance, I installed a Wolff XP extractor

spring.  Accuracy is great and function has been 100%.  Nicest uppers I've ever owned.