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9/22/2017 12:11:25 AM
Posted: 7/31/2003 6:59:14 PM EDT
So a rock river arms or armalite mid-length uppers are more reliable than a colt or bushmaster?
Link Posted: 8/1/2003 7:46:42 AM EDT
WES, anyone
Link Posted: 8/1/2003 7:56:41 AM EDT
Uhh, Colt and Bushy don't make mid length uppers.
Link Posted: 8/1/2003 8:12:13 AM EDT
Originally Posted By G-CODE: Uhh, Colt and Bushy don't make mid length uppers.
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no kidding,
Link Posted: 8/1/2003 8:17:20 AM EDT
Evidently I read your question wrong, sorry about that.
Link Posted: 8/1/2003 8:19:17 AM EDT
need more coffee
Link Posted: 8/1/2003 8:30:26 AM EDT
Originally Posted By mikepenn33: need more coffee
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Not enough diet pepsi and my reading comprehension skills go to hell. You do have a good question, even though the differences [b]may[/b] be very minimal.
Link Posted: 8/1/2003 8:51:33 AM EDT
I've never heard that. The only reasons I bought one was a longer handguard, longer site radius, you could actualy use a bayonet if so inclined and it looks a lot better.
Link Posted: 8/1/2003 8:58:10 AM EDT
They claim they are. Armalite has a blurp about it on there website. Makes sense. Although I never experienced problems with my short gas system (maybe in full auto the problem arise).
Link Posted: 8/1/2003 9:17:01 AM EDT
I think I found it it's in the tech notes section of there website. Here's a snip of the write up, take it for what it's worth. [url]www.armalite.com[/url]
Technical Note 48, The Effects of Barrel Design and Heat on Reliability Background: The M4 Carbine has developed a reputation for poor reliability. The excessive malfunction rate of the M4 Carbine is due to physical imbalances in the mechanism itself, exacerbated by heat. Analysis of the problem requires a good understanding of the carrier group and barrel of the rifle, and the functions of the cartridge case. Facts: Relation of carrier group design, barrel length, gas port location, and propellant gas pressure. The distance from the chamber to the gas port, the length of barrel beyond the port, and the pressure of the propellant gasses determine the amount of energy provided to the action of the M-16 series rifle. The heart of the M-16 operating system, the carrier group, was designed to function well with the original 20 inch long barrel of that rifle. A change in the cartridge (bullet weight or powder), the length of the barrel, or the location of the gas port along the barrel can substantially change the pulse of gas that enters the carrier group and drives the rifle action. Short versions of the M16 (including the M4) suffer from relocation of the gas port and changes in barrel length. The carbine gas port is located closer to the chamber than the gas port of the rifle: 7.5 inches instead of the 13 inch distance on the rifle. The gas pulse therefore enters the gas tube sooner and reaches the carrier group earlier than it does in the rifle length barrel. In addition to reaching the carrier sooner, it reaches it at higher pressure. The gas pressure at the carbine’s gas port is double that of the rifle: 26,000 psi vs. 13,000 pounds per square inch. The early pressurization of the carrier causes the carbine to begin to extract earlier than the rifle does. At the same time, the gas in the carbine’s carrier is of higher pressure than it is in the rifle, and it forces the carrier to move the rear at a higher velocity than it moves in the rifle. Because of the earlier extraction, the cartridge case has less time to transfer heat to the chamber wall and shrink away from it before extraction begins. The cartridge case has a tendency to stick to the chamber wall, and resistance to rearward movement is high. When the bolt, drawn rearward by the high velocity bolt carrier, tries to pull this stuck case to the rear, both the extractor and cartridge case are heavily stressed. The resistance can cause the whole mechanism to become sluggish or stop, or to cause early failure of the extractor or bolt. As discussed above, the distance from the chamber to the gas port is important. So too is the length of the barrel past the gas port. That’s because the bullet serves as a plug to keep the gas pressure trapped in the barrel so that some of it can pass into the gas tube and back to the carrier. If the length of barrel beyond the gas port is too short, so is the “dwell” of the plug in the barrel. The gas pulse supplied to the carrier can be too short to deliver all of the energy that the carrier group needs. Too long a section of barrel beyond the gas port can cause too long a gas pulse. Carbines with 11.5 inch long barrels have a very short segment of barrel beyond the gas port and the gas pulse is thus shorter than the carrier group requires. This problem combines with the carbine problems already described, and the reliability of carbines with 11.5 inch long barrels is somewhat poorer than carbines with longer barrels. Efforts to adjust for the short barrel by enlarging the gas port produce a firearm that is extremely sensitive to differences in ammunition. Efforts to correct the problem by using different springs or buffers or by changing the volume of the gas used are only partially successful. The faster movement of the carrier group in carbines also creates an interesting and largely unknown problem with the extractor. Most of the extractor’s mass is ahead of the extractor pin. The bolt turns to the unlocked position so fast that centrifugal forces tend to cause the front end of extractor to fly open, and it disengages from the cartridge . The faster movement of the M4 bolt increases this centrifugal force and the extractor tends to stay open longer than it does in the rifle. This tends to decrease extractor efficiency and increase extraction trouble. Correcting basic carbine weaknesses: 1. Reduce the diameter of the gas port to reduce high pressure gas flow to the carrier. This can render the mechanism somewhat more prone to powering problems than the larger gas port of the rifle. 2. Provide an expansion chamber to buffer the gas flow and/or store gas to power the carrier. Such chambers tend to cool the gasses and can become clogged with powder residue over time, reducing the buffer effect. The flash hider of the Vietnam-era XM177 Carbine provided a buffer effect and stored gas. 3. Shift the gas port. ArmaLite® has shifted its carbines gas port two inches forward compared to the M4 Carbine. Since the commercial minimum barrel length is set by law, this change serves reduce the gas pressure, delay its transmission to the carrier group, and reduces the length of barrel (and thus gas pulse duration) beyond the gas port. This change is easy in a commercial setting but has logistics implications for the military. 4. Decrease the tendency of the extractor to open by increasing extractor spring strength, adding material to rear of the extractor to reduce the tendency to open, or adding various elastomer forms to the extractor to reinforce the spring.
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Link Posted: 8/1/2003 9:59:58 AM EDT
Odiously the longer the barrel the better back pressure you have to work the action, however I don't think any one is better then the other if properly tweaked. I have made factory faulty 10.5" 11.5" and even a 7.5" barrel run. It all comes down to looks, long, short or medium hand guards to each his own.
Link Posted: 8/1/2003 4:08:23 PM EDT
Link Posted: 8/1/2003 4:32:22 PM EDT
The mid-length gas system places the gas port at 9.5 inches, versus 7.5 for the carbine and 13 for the rifle -- The extra length does, imho, make a difference. The gas pressure is considerably lower at the mid point, the cycleing starts later and the bolt velocity is lower... all contributing to a more reliable and smoother gun. Keep in mind, that the extra 2" of barrel also means 2 more inches of gas tube. FWIW... We are in production with a M4 mod that uses the mid length system and still mounts the bayo, for those who that is important to?
Link Posted: 8/1/2003 5:19:36 PM EDT
Troy: The difference on mine is only 1/4" shorter from the front site base on a standard 20". The bayonet ring mounts on the actual flash hider instead of the back ring but it mounts pretty sturdy. I have a flat top gas block with a clamp on bayonet lug.
Link Posted: 8/1/2003 5:59:36 PM EDT
Gunzilla, I've been trying to e-mail you about starting the midlength upper we discussed. Get back to me as your e-mail seems to be an issue for me. Thanx. [:)>]
Link Posted: 8/1/2003 6:07:57 PM EDT
What about the pigtail gas system. I believe its about as long as a rifle pipe. I've thought about buy one but I've never had problems with my 11.5 setup. Are they any good or just a waste of money?
Link Posted: 8/1/2003 8:02:13 PM EDT
Link Posted: 8/1/2003 9:26:55 PM EDT
I suspect that a pig tail tube on an 11.5 upper may not work good like it does on an M4 b/c you might have too little barrel after the gas port relative to the volume of the gas tube. Understand? But if the pig tail would work there I would preferr it to slow down bolt velocity.
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