PIGTAIL GAS TUBE PROBLEM


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Oscar1
March 4, 2007, 07:47 PM
Just got back from the range after installing a pigtail gas tube. The rifle is a bushmater XM-15E2S(16" CARBINE). When fired the bolt carrier does not travel far enough to eject the shell. I used 3 different types of ammo including some hot varmint loads. Is it a spring issue or what. The installation tips that came with the gas tube mentioned using a lighter spring.
Anyone know what I need to do?

Oscar

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rbernie
March 4, 2007, 08:06 PM
Take the pigtail back off and put back the tube that was working? :p

If you really want to run the pigtail, I'd start by looking for soot or carbon buildup around the gas block to see if you're losing pressure there. Altho I'm sure that it's contraindicated by formal MilSpec armorer's manuals, I usually use some non-hardening gasket sealant (Permatex) around the tube when I install it into a gas block and around the barrel's gas hole when installing the gas block onto the barrel.

Bartholomew Roberts
March 4, 2007, 08:43 PM
Pigtails are usually used to make shorter barrelled carbines (10.5") run more reliably. Putting one on a 16" probably reduced the gas flow too much and you either need to use the original gas tube or go to a lighter spring and buffer.

You might also follow rbernie's advice and look for some gas leakage around the gas port. Also check to see if the gas key and gas tube are mating up well.

Oscar1
March 5, 2007, 07:09 PM
So if this tube reduces the pressure too much how does the full length rifle work? The reason I put it on in the first place was to try to bring the pressure down a little closer to normal.

Oscar

Bartholomew Roberts
March 5, 2007, 08:47 PM
The full length rifle works just fine; which is more than I can say for several of the fatboy and pigtail gas tube mods I've seen. They are generally designed to correct a very specific problem. If you don't have that problem, then the regular gas tube is usually better.

rbernie
March 5, 2007, 10:13 PM
Does the carbine run a stiffer spring rate in the action spring as a result of its gas design? If so, that might account for the difference between a rifle-with-a-rifle-length-gas-system and a carbine-with-a-rifle-length-gas-system.

Bartholomew Roberts
March 5, 2007, 11:00 PM
Carbine runs a different buffer weight and a different spring length than the rifle (as well as a shorter buffer); but it shouldn't make a difference as you can run a telestock on a rifle length gas system with no problem.

rbernie
March 5, 2007, 11:14 PM
it shouldn't make a difference as you can run a telestock on a rifle length gas system with no problem.Yeah, there is that. :o

44AMP
March 5, 2007, 11:35 PM
Port pressure. Original 20" barrel, straight gas tube, buffer x and spring tension x, all calculated to provide reliable function with gas port pressure x (provided by ammo loaded with xxx)

First M16 reliability issues show up after change in ammo spec (powder type), which changes gas port pressure.

Now, take the carbine, 16" bbl. gas port pressure is different from rifle, due to being taken at a different position on the barrel. Straight tube still works, with adjustment to buffer and spring tension.

Then look at the really short barrels (M4). Gas is tapped much closer to the chamber. Buffer/spring adjustment isn't quite enough, so the "pigtail" gas tube is developed, to "mimic" tapping the gas further from the chamber. Without the balance from the buffer/spring combo proper for the pigtail tube, functioning becomes erratic.

The real question is, (if) your carbine was working properly, why did you change it?

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