I am looking to build a 16" barreled mid length, and would like some input on this. Pros and cons for this kind of set up. I have chosen Armalite for their chrome lining, but would also like to have the barrel without a brake (which Aramilite can provide) and in a light weight profile. Thanks for your help on this.

Be sure it's chrome lined, not all ArmaLite barrels are.

The "mid length" refers to a nonstandard set of handguards and gas system.  There are no advantages to the system and being nonstandard there are always potential liabilities.  

This setup may be more cosmetically pleasing (to some) but my rifles don't care if they're fashion statements or not.

-- Chuck

Thanks Chuck this gives me some food for thought, which is what I am looking for. Have contacted Bushmaster and some time in 2003 they will be making 16" light weight post ban barrels
may just wait for one of these. I have a 16" XM15-E2S, but it seems too barrel heavy. In the 1980's had several colt carbines and if memory serves me the lighter profile balanced better for me.

I believe that Armalite would argue the point that there are no advantages to locating the gas port farther from the chamber.

Joe --

Contact Kurt Wala.  He can turn your 16" HBAR barrel to whatever profile you desire, and reparkerize it.  Want it to look M4-ish?  He can do that?  Want just a thin profile?  He can do that too.  Want a faux compensator on the end?  Yep.

Kurt has done two barrels for me and both were first class jobs.  My favorite is the Lightweight Dissipator he made.  It's just about the same weight as my M4 barrel.  Your 16" carbine can be even lighter if you want a thin profile.  

I'm sure ArmaLite claims their system is just as reliable and it may be, but it's proprietary.  You need special ArmaLite handguards, and a special ArmaLite gas tube if anything needs to be replaced.  And all the troubleshooting guides (TM9-1005-319-23&P) assume standard parts.
-- Chuck

Chuck:
I have thought about some of the same things for the Bushmaster, and may just send it out to have it turned into a light weight. I also have 2 RRA lower receiver's on the way one will be for a J&T 20" expedition kit. The other one is still up in the air as far as the upper. In the early 80's I held an FFL and built many AR's in the A1 config, it has been a long time and much has changed since then, guess I am trying to get a feel for all of this. This board has been a great help I have learned a lot of new info and refreshed the things from the past. Thanks for the help all of you.

Joe --

I never even saw my Dissipator before it became a lightweight.  I purchased the barrel from Gunsmoke and had it drop shipped to Kurt who modified it and sent it to me.

With a vice and a few simple tools you can swap barrels in 15 minutes.  The base barrels run about $200 so if Kurt is running a backlog you may want to have him modify a new barrel rather than your only shooting barrel.

Few Bushmaster, Colt's, or ArmaLite rifles need help here in the Troubleshooting section.  Can't say the same for J&T and the others.....

-- Chuck

I have to disagree with this statement.  Ergonomics of the midlength handguard is better suit for taller/longer limbed individual.  The midlength design has a better sight radius over the standard carbine design.  Plus the midlength design give a marginal increase of bullet velocity.  Rock River Arms also make a midlength design as well.

Just my $.02  

Which sentence do you disagree with?  [;)]  The parts are certainly non-standard.  Non-standard parts aren't proven and have the potential for problems.

Increased sight radius has no advantage unless you're shoting at Camp Perry.  Certainly a 2" sight radius would be pretty lame, but the standard carbine sight radius is accurate well beyond 300 meters, farther than many of us can see targets.

Longer handguard is a minor enhancement, but this was done for cosmetics, not to enhance the shooting system.  It's an attempt to create a market niche.

Bushmaster Dissipator provides an even [i]longer[/i] sight radius and handguards and makes it pretty hard to grab a hot barrel.  Not as [i]pretty[/i] as the mid-length barrel, but uses proven stock parts for the gas system and handguards.

Rather than produce another Dissipator knockoff ArmaLite produced this one.  

-- Chuck

Les Baer Custom also makes a mid length AR upper assembly. They make a mid length gas tube that is 2 inches longer than a carbine length gas tube and also make barrels with the gas hole placed 2 inches farther out on the barrel to match. There are also mid length free float handguards for this. There are actually several makers with mid length parts available. They are not as popular or well known, but they are available.

Let me begin by saying I've carried on type or another of the m4 since 1992(727-m4a1-CQCR), and am painfully aware of its short-comings with extremely high use rates.(1500rd + a day)
The mid-length provides many advantages, ergonomic, engineering, and to some cosmetic. It is much closer to the original design perimeters when calculating gas pressures, and mechanical timing.
Having the front site two inches out makes the front sight relatively smaller, for a perceptive benefit. The front sight assembly also takes up much less space, in the optic's FOV, when an ACOG is mounted.
The increased length of the gas tube provides a reduced peak pressure with lengthed impulse. In short it will more reliably cycle, esp. extract. Additionally it takes a bit longer to heat up the upper receiver.
Addmitedly I think it looks better, form follows function.
If during my years working for Uncle Sam I worried about "non-standard" parts replacement, instead of I'd of been lumbering around with many pounds of outdated inneffective gear the conventional troops were stuck with. Choose wisely and test your gear. Common sense goes a long ways.
I've yet to see a gas tube or handguard set fail and can't imagine it in civilian use. All the important parts are standard. If you must get and extra hand guard & gas tube. I'd spend my money on an extra bolt group.
Presently I have a RRA middy upper and will be buying a Armalite chrome-lined too. I'll have it sent off to be reprofiled to lighter specs.

Just to further the point made by sar3k, the reason that Armalite, Les Baer, and others are going to the 2" longer gas systems and handguards is to INCREASE reliability and function of the weapon. Sar3k is exactly right when he states that the original design of the AR15/M16 used the 20" barrel with a gas tube of a very specific length to ensure proper timing of the gas reaching the bolt carrier at the proper time (after the cartridge case has contracted and is no longer gripping the chamber walls). The weapon was never originally intended to have a shorter barrel. Problems occur when you shorted the barrel along with the gas tube length. What happens is that the gas charge hits the bolt carrier too soon - when the case is still partly expanded and gripping the chamber walls. The extractor will then slip over the rim of the case (or pull through the rim) leaving the case in the chamber, or only partially extracted, and causing a double feed. A common "fix" for this has been to increase the strength of the extractor spring - so it won't pull over the case rim and will rip out the case even with it partially clinging to the chamber walls. The springs do help - but are only a band-aid, and do not address the real problem of the altered gas timing. tThe 16" and 14.5" barrels have the same length gas tubes, and are on the "ragged edge" of functional reliability. This is why you don't see many 12", 10", or shorter weapons very often now days in the military or police department SWAT teams - too many malfunctions, even though the short length would make ideal entry weapons (additionally, the shorter barrels decrease bullet velocity to where the .223 rounds don't fragment like they should and decrease the wound ballistics and therefore the effectiveness of the rounds, but that's a different topic). Anyway, what Armalite is doing with their 2" longer gas tubes is to solve the gas timing problem by extending the length of the tube closer to the original design parameters, therefore correcting the PROBLEM with the short barreled guns, not just attemting a quick fix by using a stronger extractor spring. The longer handguards are only to cover and protect the longer gas tube, and to make it have a more standard appearance. So - the longer gas tubes are actually making the short barrel guns MORE STANDARD when you consider the original design of the gun, and therefore make it MORE reliable. One other side note - this is also the purpose of the M16 Pigtail gas tube, which is an aftermarket coile gas tube which winds around the barrel. This design uses a longer tube on a regular short barrel gun to solve the function problems.
hope this helps
Doc

Wow, Swatdoc.  Do you ever make me feel lazy.

That's a wonderful compilation of information you've written up.  And sar3K too.  Great job, both. [:)]

Reading these posts has confirmed many of the things I was looking at in a mid length barrel.
One just has to fire a 16" and a 20" barrel to feal the differance in cycle rate. The 16" just plain cycles the action faster and harder. As I return to my old intrest in AR's there is a need to know what works best, and is the best for me. As this will be my third rifle a Armalite 16" mid length will give me a chance to explore yet another area of this great rifle.      

IF your really into this, read Accuarcy speaks book about building AR's.Whole section on gas bleed ports.

I had compass lake engineering build my custom 18" barrel, I sent them a gas tube from mid length armalite setup. Someplace I found the gas port size.

Works great!!!! The pigtail tube is sorta half way there. Pressure is still tapped to early in the barrel.

RRA and ARmalite are great carbines!!!