Datebase of gas tube diameters?

AR/M4 AR Technical Discussion
1

I have a 16: carbine-length AR and a 12.5" mid-length AR. Both are run suppressed full time (YHM T3). The 12.5" has a off the shelf Luth-AR tube on it and is very gassy. The 16" is in process, but will have a BCA off the shelf carbine tube as of now

I tried the BRT tube route & they sent me a tube with a .067 port and that was so msall that the gun would not cycle.

I know I can go adjustable gas block, but hoping someone has some sort of factory gas tube diameter database or chart so I can perhaps find a smaller port tube to reduce gas.

2

Which barrel did you try the .067 gas tube on?

3

The 12.5"

I’m not looking to rehash the BRT junk or find another custom tube. Just hoping to find some info on factory tube sizes so I can possibly try other diameter tubes vs what I have now.

4

Is the 12.5 carbine length? My 11.5 carbine length barrel is set up for 50/50 suppressed unsuppressed and cycles with a .067 gas tube. It would certainly cycle suppressed.

5

No, mid-length

6

The beauty of an undersized tube port is that you can open it up a little yourself. I’d rather start too lean and work up. But that’s my brain.

7

There is no other gas tube that will do what you’re looking for. They all have ports larger than the port in the barrel.

2 Likes
8

I know they are larger. I’m wondering if any companies make their ports smaller than others

9

Yeah, BRT. You can order them in any size you want.

10

You clearly did not read my OP. Good day

1 Like
11

Like 1168 said, all standard tubes have openings way bigger than the barrel port.

With the price of the BRTs, I still vote for opening up the tube you have .002" or so.

1 Like
12

Once again, I know they are bigger & I already stated BRT was junk.
I am simply asking if all standard gas tubes are the same diameter or do some companies make the port smaller than others? If yes, who?

13

As far as I know, all gas tube ports are the same at the gas block end.

BRT is the original innovator in respect to have a size you can order.

14

There are reasons the standard 1/8 inch hole is used in the gas tube, first, the tolerances on the location of the cross pin can be much looser and still have adequate hole over-lap without excessive reduction in area. The second reason is the only restriction in the gas system is the gas port in the barrel.

Using the gas tube as a restriction (under-sized hole in the gas tube) is a poor idea. High temperature, high pressure gas is erosive, it will eventually erode the barrel gas port, but this take several thousand rounds, if the gas tube is used as a restriction, it will erode. The gas tube is thinner, and made from a softer material, and will quickly erode to where it is not the smallest restriction in the system.

15

YHM makes a restricted Gas Block. They ship at .065 IIRC.

They tend to bleed some at the gas tube interface so it may not give the most accurate results until it seals up.

You can open the port through the rear set screw hole.

The BRT Tubes are not junk. Sometimes they need to be opened. They will erode but at best it takes several thousands of dollars in ammo to do so.

The YHM restricted blocks have almost no erosion with heavy use. They are setup to work without a handguard cap.

17

What problem have you had with them, 6midgetsandmayo?

18

Dude, you are making everybody’s head hurt. You ask if there is a difference in gas tube port diameters between manufacturers and that you want to try a smaller port. BRT specializes in providing just EXACTLY what you are asking for, a tube with a smaller port. Am I missing something? I re-read your post several times to try to figure out what you are after.

Maybe get a set of tubing benders, flip the tube over, reshape it and start drilling until you have a custom tube tuned to your application.

19

Adjustable gas block will solve most, if not all, of the problems. Can’t have that? I was in that situation with an A2 FSB, because I didn’t want to pay the money for an adjustable FSB, there is alternative.

I tapped screw threads in the orifice in the FSB. A short stainless steel set screw was installed there as gas bushing. Different size of hole drilled through the set screw provides the level of gas restriction needed. It works great in my A2 clone. Not my invention but an idea borrowed from mini-14 folks.

The BRT gas tubes? I need to run a high fever to spend $60 for that. Can’t you just rotate an ordinary gas tube 180 degree and drill your own port?

-TL

20

No, there’s two bends in an ordinary gas tube. As for the cost, there’s a slight discount for being a member here, and the price is competitive with an AGB. I like to assemble my own uppers, so I’m buying a gas tube or gas block anyway, thus only look at the delta vs a reputable non-restricting part. And at this point I have some lying around.

The setscrew method is cheaper, of course, if you already have the required tools. There’s also the YHM block that comes with a restricted orifice.

21

Bending the tube is not that hard. I do it all the time. Ordinary gas tube costs <$10 each. I can get adjustable gas block for <$30 each. Not the fancy type of course, but plenty enough to serve the purpose, at least much better than keeping swapping out gas tube with different port sizes.

To make the bushing, I paid $15 for a extra long tap. That’s about it. Set screw is like 20 cents each. A set of numbered drill bits does cost more, about $40. Still kicks the butt of $65 gas tube with small port hole.

-TL