Straight pistol length gas tube

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JDNC
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Re: Straight pistol length gas tube

Post by JDNC »

JDNC wrote:
Jim Timber wrote:Every AR15 gas tube I've ever handled has had a ball swaged into the end of it. The area before the ball is drawn down so it doesn't have added friction on the gas key. The radius on the end is to prevent it from scraping as it follows the chamfer in the key's inlet hole (compensating for minor misalignment), and preventing fouling from building up and jamming it from excessive friction.

I'm not trying to tell you not to do it, I'm just looking at the obstacles you face in the process from my perspective.
I'll look at this again. I ordered a pistol length tube and miked it, maybe I missed something or have a defective tube to begin with.

Thanks, JD
This is the key end
Image

GB end
Image

And the relief section
Image

Do you think this is defective, or what? I can't wait to get the rifle tube to compare.
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Jim Timber
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Re: Straight pistol length gas tube

Post by Jim Timber »

Mine measures .164 behind the ball.

Image

This one has 4K rounds on it or so and is as it was removed from the gun.
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JDNC
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Re: Straight pistol length gas tube

Post by JDNC »

Jim,

What's the GB end measure if you don't mind.

I got to thinking about this thing, and I don't know if the smaller section is drawed down to a smaller diameter or turned down. If it's been drawed down smaller the wall thickness may not have been altered that much, but if I turn this down it may make the tube too thin. I think I'm going to cut the rifle to tube to length and chamfer the end and try it.

JD
JDNC
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Re: Straight pistol length gas tube

Post by JDNC »

I think the relief behind the end may be to aid in handling carbon build up. I think I will duplicate the pistol gas tube in reference to this contour and just leave it straight and cut it to length.

JD
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Jim Timber
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Re: Straight pistol length gas tube

Post by Jim Timber »

.175

I mentioned the fouling in a previous post, that is correct.
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dellet
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Re: Straight pistol length gas tube

Post by dellet »

JDNC wrote:Jim,

What's the GB end measure if you don't mind.

I got to thinking about this thing, and I don't know if the smaller section is drawed down to a smaller diameter or turned down. If it's been drawed down smaller the wall thickness may not have been altered that much, but if I turn this down it may make the tube too thin. I think I'm going to cut the rifle to tube to length and chamfer the end and try it.

JD
I am probably over thinking this. My question is if the inside profile of the tube is the same as the outside?
If it is the same hourglass shape, then there will be a Venturi effect on the gas traveling through the tube which would need to be considered also.
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Suputin221
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Re: Straight pistol length gas tube

Post by Suputin221 »

Jim Timber wrote:How are you going to seal the front end of the tube when you cut it down?
You cut the other end off. :roll:

Jim Timber wrote:So I'm going to assume you have pipe swaging tools to reproduce the ball end that ensures a proper seal in your gas key?
What? How about just throw it up in a lathe and turn off a small amount of the OD? I've done this on a number of gas tubes and it works fine. Why go crazy re-engineering the world when a simple solution will do?

JDNC wrote:One question, does anyone no the purpose for the the relief (smaller dia. section) on the gas tubes?

I mean I can can duplicate it, but why? Does it need clearance through the receiver or key?
Try pushing a gas tube through the upper and you will find out why that relief section is there.
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Re: Straight pistol length gas tube

Post by Suputin221 »

JDNC wrote:
Jim Timber wrote:Every AR15 gas tube I've ever handled has had a ball swaged into the end of it. The area before the ball is drawn down so it doesn't have added friction on the gas key. The radius on the end is to prevent it from scraping as it follows the chamfer in the key's inlet hole (compensating for minor misalignment), and preventing fouling from building up and jamming it from excessive friction.

I'm not trying to tell you not to do it, I'm just looking at the obstacles you face in the process from my perspective.
I'll look at this again. I ordered a pistol length tube and miked it, maybe I missed something or have a defective tube to begin with.

Thanks, JD
No, you are correct and he is wrong. The "ball" on the end of the tube is not a ball at all because it is the same OD as the rest of the tube. All you need to do is turn down the OD of the tube a bit to replicate the undercut section. He is wildly overthinking the entire thing when all that is needed is a very simple solution. I've done a bunch of these and they work fine.
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Re: Straight pistol length gas tube

Post by xacex »

I will watch this thread with interest. Picked up one of these barrels when they were down to 155$. I was planning on using a JP JPGS8 which looks like it will take a standard gas tube. This is my third blackout. Like I needed another one, but I didn't have a pistol gasses carbine to play with different powders. The gas block in question looks nice. It was hard finding an adjustable bull barrel gas block that fit under a rail for some reason. Not much demand for such a beast. If I had to cut a gas tube down I would follow the advice here, and cut the block end, weld it up,shape, and drill the port and roll pin holes. The larger diameter at the upper end is there to help pump out water if the gun is submerged.
JDNC
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Re: Straight pistol length gas tube

Post by JDNC »

Update:

I was advised by SLR that none of their handguards would go over the DA9 GB. They advised they would be offering a new DA version possibly in March that would go under there existing handguards. I've been looking at Yankee Hill and think their guards might work.

Any ideas?
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