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Pigtail Gas Tubes!?!?

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#1 eringobragh


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Posted 26 April 2006 - 07:25 PM

Was thinking of trying a pigtail gas tube in my M4. I wanted to run one in conjunction with my Enidine buffer, but heard now that they (m16 Clinic...maker of the tube) do not suggest using with a hydralic buffer. Will I see short strokes if I use the two together, or other possible problems?
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#2 bberkley


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Posted 26 April 2006 - 09:26 PM

If I recall, you only need the pigtail tube if you run a short barrel where there isn't much barrel forward of the gas port.

Spend your money on ammo.

Whats wrong with the normal carbine buffer?
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#3 uscbigdawg


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Posted 26 April 2006 - 11:55 PM

Using the SEARCH, plugging in Pigtail, I found these:

Pigtail Discussions

SPC (P) Richard A. White, Senior Medic
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Richard (Rich) A. White

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#4 eringobragh


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Posted 27 April 2006 - 06:25 AM

I cancelled the order for the Pigtail...thanks for the info guys! I see people talking about the PRI Fatboy tube...any thoughts? PRI also states to use with standard buffers...how do you think it would react with an Enidine buffer?
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#5 wsimpso1


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Posted 27 April 2006 - 10:58 AM

What are you trying to fix? If it is unreliable, that is one thing, if you want quicker recoil recovery, that is another.

Let's think for a minute how the AR15 mechanism works. The bullet is shoved down the bore by a bunch of hot gases. After the bullet goes by the port, these same hot gases start flowing down the tube, and a wave travels at the local speed of sound in the gases (gun gases are hot and thus have much higher speed of sound than the air around us). When this wave reaches the carrier it commences to accelerate the carrier and buffer backwards, then hits the cam pin, unlocking the bolt, pulling the case out of the chamber, blah, blah, blah...

In a 20" barrelled rifle, the gas port is about 4" from the muzzle, and the bullet is long gone and the gun gases have largely drained from the chamber by the time that the bolt actually starts to pull the case from the chamber. Gene Stoner and Armalite, and then Colt and the Ordnance folks worked out the gas port size and free travel of the carrier before it starts to open the bolt and extract the empty case, so the timing is pretty good and it works very reliably.

In the CAR15, with the 11" through 14" barrels, the timing of everything was still pretty good. The bullet leaves shortly after the gas pulse starts down the gas tube, and again, it worked pretty reliably too.

Along comes the rule that civilian barrels can not be less than 16", so the makers used 16" barrels but kept the port in the same place where an 11" gun would have it. The bullet goes a long ways (and takes a longer time) after the gas pulse starts down the tube, and what do you know, some shorties try to yank the case from the chamber too soon, and they short stroke (too much carrier energy is used up getting the case out of the chamber leaving too little to run the carrier all of the way back), rip rims off cases, etc. Some shorties are reliable with only certain ammo, others work fine, and others just do not want to behave at all.

The logical solution is to place the gas port closer to the muzzle, and we do have makers of 16" barrel systems with mid length handgaurds and there is more sight radius too. But many makers still do the CAR length handguards and gas tube and front sight base position... What's a mother to do?

So along comes some guys that want their shorties to work, and learning what I just described to you guys about timing, came up with ways to delay opening. One of them comes up with the pigtail, which puts a long gas tube on a short space, thus delaying the carrier movement until chamber pressures have come down, and another guy comes up with a larger diameter gas tube, which causes some expansion and thus lowers temperatures, reducing the local speed of sound in the tube, which also delays opening a bit. Pretty clever, huh? In both cases the duration of the pulse is somewhat extended by these changes and total impulse driving the carrier/buffer is lower too (energy is lost in the process). The combination makes the opening occur a little later, and they work for making unreliable shorties more reliable. Of course, polishing the chamber and feed ramps might help quite a bit too.

Then somebody else comes along with the idea to slow the cyclic rate and reduce recoil. They build a different buffer/weight/spring system that dissapates some of the energy acting to move the carrier and buffer hydraulically. The potential problem with that is that the Enidine for shorties is likely set up for the standard gas tube. Add one of these systems that delays things a bit and reduces the total impulse to an Enidine, which also dissapates energy, and the combination may result in short stroking...

So, If you want a shorty to stop ripping rims, try a fat tube or a pigtail.

If you want less recoil, maybe the Enidine is the ticket, or a light JP carrier. I would definitely apply a good brake to the muzzle if I wanted faster recovery. If combining the Enidine and a Pigtail does work fine, great. Combinations of non-standard parts and the Enidine, well, I would rate them most likely to act up. If they act up, and you have checked chamber shape and size and throat length and polished the chamber, then maybe a slight enlargement of the gas port is in order.

My shorty? It works fine with a polished chamber, but if I were to replace the barrel, it would get a mid-length handgaurd set (then polish the chamber and ramps). My competition gun? It has a Miculek Brake and GI gas tube/bolt/carrier/buffer system and a polished chamber and ramps. Works great. Light carriers? Adjustable gas blocks? UGH!


Good Luck

#6 ken hebert

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Posted 06 May 2006 - 06:30 AM

Good post. Thanks for expanding my AR knowledge.

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#7 Wakal


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Posted 06 May 2006 - 06:56 AM

I have a pigtail set up on my 7" SBR AR15...without it, the rifle just didn't cycle correctly. With it, no problems.

My 16" Open AR has an adjustable gas tube because felt recoil was a bit harsh with a JP light stainless carrier so I needed to turn the gas down a bit ;)


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#8 gunny


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Posted 06 May 2006 - 08:30 AM


Lots of good information I didn't know.

Very informative, thank you!

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