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9/19/2017 7:27:10 PM
Posted: 10/23/2002 6:25:36 AM EDT
Hey all,

I'm in the process of "spec"ing out my first AR-15 to build at home. I've come to the conclusion that I love the 16" carbine barrel length, but I'm not a fan of the short CAR handgaurds. Then I stumbled onto this ad for a rife auction and I was sold on the "mid-length" hand guards.

http://www.gunbroker.com/auction/ViewItem.asp?Item=5496952

My question: Do I have to custom order a carbine upper from JT or M&A that has the mid-length hand guards, or can I order one of their kits, and replace the hand guards myself. It seems to me there is a fixed hole in the barrel that the gas block is bolted over, and this would mean the barrel would need to be built for these longer handguards from the start.

Any advice on where to source a mid-length handguard carbine upper would be much appreciated.

Thanks.
BWhalen
Link Posted: 10/23/2002 7:05:31 AM EDT
I have a 16" DPMS AR15, and I recently purchased the new DPMS 4 rail (RAS-style) standard length handguard for it. I too disliked the carbine length handguard - just too short to add anything worthwhile.

Anyway, I've had some trouble with the handguard because of the bull barrel, but DPMS is fixing it for me. With the new free floating handguard in place, I will only have about 4" of naked muzzle - which I don't see as a problem. Pleanty of room for my forward pistol grip, flip up BUIS, bipod, etc.

The DPMS handguards may not yet be on their website, but you can call & order them directly.

If you are looking to maintian the "stock" M16 handguard (non-free floating) look, sorry.
Link Posted: 10/23/2002 7:22:04 AM EDT
[Last Edit: 10/23/2002 10:57:15 AM EDT by Quarterbore]
The Mid-Length Carbine grips are one of those items that make so much sence that it is amazing to think that they were not made much earlier.... BUT THEN .... when Armalie finally did come up with the idea they did it wrong!!! I will try to explain....

I have a page on my website for a project that I am trying to work on. See: quarterbore.com/300whisper/300upper.html which covers much of what I am going to describe....

As I am sure you know, a 20-inch M16A2 and a 14.5-inch M4 Carbine will both mount a M-9 bayonet the way a bayonet is supposed to be mounted...



While a 16-inch barrel will not mount a bayonet as the Bayonet Muzzle Ring will be around the barrel and will flop around! The obvious fix was to make a mid-length carbine grip that would move the front sight base forward to where it needed to be for the bayonet to properly mount! For a reason I will never understand, Armalite SCREWED THIS UP as their mid-length upper is about 11/16-inches too long! What this means is if you have a RRA or Armalite Pre-ban Mid-Length Carbine upper, the Bayonet "MUZZLE" Ring will mount about 2/3 down the length of the flash supressor... IT JUST LOOKS STUPID plus it would not be anywhere near as strong as if it were located in the areas of the threaded barrel where it is supposed to sit!

So, in a long winded answer, I would suggest that you consider looking for a proper length Mid-Length grip and have a gunsmith make the barrel for you with the gas port where it needs to be! You can also use a LOW-PROFILE gas block as MSTN sells which will allow you to use a longer forend tube with a gas block that would be under the grip. This would not work so great if you want to use iron sights unless you then add a flip up sight onto the top rail of a Mil-Spec-1913 rail grip...

If you have a post ban, well then the whole bayonet issue isn't an issue... You can buy a INCORECTLY LENGTHED Armalite or RRA Mid-length upper that will be all set up for you.... Armalite even sells just the barrel so you could build your own with the gas port where you need it!

Hmmm, now what was the question.... Sorry so long winded! Please let me know if you are confused and I will try to help...
Link Posted: 10/23/2002 9:49:04 AM EDT
Quarterbore - always interested to hear what you have to say. I did one of the things you mentioned; I put a standard length handrail on my 16"; it completely covers the gas block. As this is a bull barrel, I never had a front site anyway (I'll be adding a flip up BUIS to the front in the future).

My philosophy was: naked barrel isn't really helping me at all, and the added length lets me put the forward pistol grip truely forward rather than practically against the magazine well. The same goes for other ad-ons - lots more room.

Any negatives to this? Of course the die-hard military-repro guys may not like the appearance, but I'm after pure function.
Link Posted: 10/23/2002 4:54:17 PM EDT
Yes, the barrel would have to be made of the handguards. You could have it move yourself, the front sight/gas block issue is complicated and would have to be smithed. Far too much trouble to be worth it.

Have you looked at the dissipator models available. This has a full length handguard on a 16' barrel. There is very little barrel exposed. you have the full sight radius of a 20" barrel. you have the compactness of the carbine. the best of all worlds.
Link Posted: 10/24/2002 7:19:46 PM EDT
I have an Armalite upper on my carbine with the mid-length HG. A very nice feature of this set-up that no one has mentioned is the position of the gas port. The carbine length hangaurds and gas port postion like we see on the M4 came about from the xm177 (colt comando)
Those guns had very short barrels and this gas port location was appropriate. For some reason when colt came out with the M4, they left the gas port in the same spot even thought the barrel was much longer. The condition is even more obvious on a 16inch barrel. Now what we are let with is a gas pick-up WAY to close to the chamber. The results: action is more sensitve to pressure spikes, cyclic rates are way too high, some actions open too fast before pressure has a chance to drop after the bullet leaves the barrel. This is why we have all these fancy gas tubes that look like pig-tails or have pressure bleed-offs or expansion tanks. The corect answer is to move the gas port out to a more friendly area like Armalite has done. I have seen a 16" barreled gun with standard rifle handgaurds and gas port location(20inch rifle cut down to 16) It worked great. The guy may have enlarged the gas port.

So I would go with a barrel designed for this port location.
Link Posted: 10/24/2002 10:00:32 PM EDT
I was under the impression that the gas port had to be farther from the muzzle. Didn't the Marine Corps do a test on the XM's and found that it was the distance from the muzzle that was important. That is why the A1 carbine was created. If there was a problem, I think Colt would have remedied that by now since the carbines have been redesigned by them at least twice since the A1 carbine of the 70's (the A2 carbine and the M4).
Link Posted: 10/25/2002 4:58:43 AM EDT

Originally Posted By knightone:
I was under the impression that the gas port had to be farther from the muzzle. Didn't the Marine Corps do a test on the XM's and found that it was the distance from the muzzle that was important. That is why the A1 carbine was created. If there was a problem, I think Colt would have remedied that by now since the carbines have been redesigned by them at least twice since the A1 carbine of the 70's (the A2 carbine and the M4).




It does cause a lot of problems on the M4. This gas port location is the largest contributor to these outrageous cyclic rates the M4 suffers from. This high rate causes decreased full auto accuracy(controllability), over-heated barrels and reliabilty problems.

I have heard that moving out to a "mid-length" gas port location can slow the gun down by as much as 100rpm

It would be almost impossible to get a major change like this on a US rifle. Think of all the RAS handgaurds they have. All the manuals have to be changed. Spare parts have to be updated and some would not be compatible between old and new guns. These are just a few reasons things don't change often there are a million more I am leaving out. All you can do is learn from your mistakes and correct them when you field a new rifle. Which is now long over-due by our standards.
Link Posted: 10/25/2002 8:23:24 AM EDT
did you see the mid-length barrels and handguards on the rock river website?
Link Posted: 10/25/2002 2:18:16 PM EDT

Originally Posted By ChrisGene:
It does cause a lot of problems on the M4. This gas port location is the largest contributor to these outrageous cyclic rates the M4 suffers from. This high rate causes decreased full auto accuracy(controllability), over-heated barrels and reliabilty problems.

I have heard that moving out to a "mid-length" gas port location can slow the gun down by as much as 100rpm

It would be almost impossible to get a major change like this on a US rifle. Think of all the RAS handgaurds they have. All the manuals have to be changed. Spare parts have to be updated and some would not be compatible between old and new guns. These are just a few reasons things don't change often there are a million more I am leaving out. All you can do is learn from your mistakes and correct them when you field a new rifle. Which is now long over-due by our standards.



Your argument of RAS and other handguards doesn't make sense. If the problems you state were that bad, they would have been inherent in the M16A1 carbine. Since then, it has been overhauled to the A2 carbine and once again into the M4. During this time, there was no RAS system. During the transition from the A2 carbine to the M4 a RAS had not yet been selected or finalized. During the transition from the A2 carbine to the M4, the new double heat shielded handguards were developed expressly for the M4. The dimensions of this handguard were not the same as the CAR handguards. During both transition phases, any major problem with the gas system could have been redesigned since they were developing a new carbine. The only criteria would have been to have the receiver parts be as interchangeable with the M16 rifle as possible. They had to change the manual for the M4 anyway because of the feed ramps. Another change for something like the position of the gas system would not have been so difficult.

Naval Special Warfare has also adopted a cyclic rate reducer that installs in the receiver to bring down the rapid fire rate. I am not sure if any other group has adopted this system, but I'm sure they are looking at it.

I am aware the XM177 had problems, that is why they developed the M16A1 carbine. if this system too had problems, they would have made the changes during the testing phase. They were going to produce new barrels for this carbine, a new handguard would not have been a big deal if they were going to make changes anyway. In a period of transition, the importance of being able to reuse XM handguards would not have been of great concern to testers, especially those in the Marine Corps.
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