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Pig tail gas tube for AR pistol build?

This is a discussion on Pig tail gas tube for AR pistol build? within the M16 AR15 forums, part of the Rifle Forum category; OK I am in the finishing stages of building a .300 BL AR pistol and need a gas tube, I would like to make it ...

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Old March 6th, 2017, 10:30 AM   #1
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Pig tail gas tube for AR pistol build?

I am in the finishing stages of building a .300 BL AR pistol and need a gas tube, I would like to make it reliable with all ammo if possible. will a pig tail gas tube help?

My barrel is 10 1/2" and uses a pistol length gas tube, I am thinking about using a "Gas Adjustable" gas block, do you think this is required?

Thanks for any help.


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Old March 6th, 2017, 11:10 AM   #2
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I built a couple of AR RIFLES in .300 FIREBALL, and a couple of 7" barreled AR RIFLES in 5.56, all using the pistol length gas port location.Only the first one had a pigtail gas tube, the other three did not need this. All of my RIFLES ended up being reliable, but this required a bit of experimentation with bolt carrier and buffer weights ( heavier was better). My experience is different than your project, because all of my AR builds had FULL LENGTH BUFFER TUBES and springs.

Hopefully some one with more relevant exoeruence will chime in.
Good luck,
Getting a short AR to function reluabky can be tricky.

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Old March 6th, 2017, 11:14 AM   #3
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No you don't need a pigtail nor will it improve performance. What you will want to be concerned about though is that the gas port in the barrel is of the correct size. I can't quote that to you off-hand, just google it. Likewise no need for adjustable gas blocks either...I think both those things are work arounds for undersized gas ports.
I built a 300 upper on an 8.5 barrel with pistol (of course) length gas and it runs 100% all the time.

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Old March 6th, 2017, 11:25 AM   #4
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My understanding about the pig tails is they are for carbine/ rifle length stock SBRs, not necessarily pistols. I could be full of ESS, though but that's the way I understand it.

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Old March 6th, 2017, 11:42 AM   #5
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look at adjustable gas blocks also

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Old March 7th, 2017, 12:31 PM   #6
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I would use an adjustable gas block way before a pigtail gas tube.

Ultimately it does come down to your gas port size... especially with it that close towards the chamber.

Pressure closer towards the chamber will be the highest... so if you had an oversized gas port ( IF ) then your BCG will be slammed pretty dang hard back..

I'd try a SLR gas block... BUT be sure what ever you use, that you can readily access the adjustment "screw".

An adjustable gas block offers the best ( IMHO ) way to tame the cyclic speed of a Pistol AR's action.

Better then buffers, springs and pigtail gas tubes.... you don't want the added mass of a heavier buffer weight, the added slam from it and a stiffer spring, causing your rifle to dip down after every shot.

I went through all that with my blowback 9mm AR.

Thinking about it... all the adjustable gas block does is restrict the volume of gas flowing into your BCG.

And IMHO.... that is the best way.

This link will show how high the pressures can be... as well as explain it.


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Old March 7th, 2017, 06:09 PM   #7
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Short answer, build it and shoot it. If it runs like you want it, great. If it needs tuning, tune it.
Your gas port size will determine if you need an adjustable gas block. Heavy buffers, springs, and anything else are work arounds if your overgassed.
If it will be suppressed, that brings up other issues.
I have seen a few perfectly gassed rifles run everything from steel case to 5.56, suppressed and unsuppressed, without the need for an adjustable gas block.
I realize your talking about a pistol, so that's going to be a little different.
I love an adjustable gas block for tuning. SLR is one of the best.

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