BCG technical spec question?

[opngrnd]

BLUF-Is there a measurement from the bottom flat of the bolt carrier to the top of the entry point on the gas key?

Backstory-I have one carrier that wants to lightly strike the gas tube on a new build. It gets worse if I apply pressure to the bottom of the bolt carrier. It wants to do the same on several other builds as well, though my Sionics and LMT carriers are fine in the new build. I've identified two things so far:
1-Gas key appears to be .0075 higher than a Sionics BCG I compared it to.
2-The internal hole in the gas key barely allows a gas tube to fit inside, although it's not a friction fit.

BCG already went back and returned once under warranty, but currently do not plan to throw the manufacturer under the bus. I picked the BCG up on the forum here while grabbing some other items I needed and was hoping it would function until I could grab a few Sionics BCGs. The manufacturer claims to hold gov contacts for BCGs, so I at least expected the bolt carrier to be good. I'll probably be out about $50, and I can live with that if needed.

[markm]

There's certainly a spec on the carrier dimensions.

But the way I see it, you could:

1. Tune (bend) the gas tube a little (to mate the carrier with the tube) like you would do on any upper build that required it. or,

2. Remove/replace the key. Possibly filing the bottom of the key to shave a few thowie off if needed.

[opngrnd]

There's certainly a spec on the carrier dimensions.

But the way I see it, you could:

1. Tune (bend) the gas tube a little (to mate the carrier with the tube) like you would do on any upper build that required it. or,

2. Remove/replace the key. Possibly filing the bottom of the key to shave a few thowie off if needed.

I'm thinking of doing one of these, but hoping to gain a little knowledge in the process. Of 4 uppers and three carriers, only one carrier doesn't work in every single upper.

What method would you use to bend the gas tube?

[Clint]

I would not bend the tube, as this breaks compatibility with other carriers, if you need to swap then around for some reason.

Also, if the key bore is so tight that the tube barely fits, it is likely to sieze up.

I had a NIB gas key lock up the gun due to this. It would not go into battery after it warmed up.

That carrier should go back to the mfg for a replacement or refund.

[opngrnd]

I would not bend the tube, as this breaks compatibility with other carriers, if you need to swap then around for some reason.

Also, if the key bore is so tight that the tube barely fits, it is likely to sieze up.

I had a NIB gas key lock up the gun due to this. It would not go into battery after it warmed up.

That carrier should go back to the mfg for a replacement or refund.

Couple questions:
1-Generally speaking, is there a direction (top/bottom/left/right) that you usually see the gas tube rest against when looking at the hole in the front of the upper receiver? In the case of this build I'm having trouble with, the gas tube rests on the bottom of the slot, possibly amplifying the issue. The BCG is least lined up with the tube when pressed up.
2-Wouldn't the BCG favor being pushed upward in the receiver due to the pressure from the magazine/rounds? I'd think the bolt locking in would minimize this.

[ScottsBad]

I'm sure there are experts here that know a lot more than I do, but there is room in the design for less that perfect alignment. However, if the gas key opening is too small or the gas tube isn't formed properly that could present a problem.

Are you having failures? Is the key banging the gas tube too hard? Because the carrier is going to move around in the receiver, and the gas tube will wobble around some too. As I see it the design is made to accommodate tolerance and operating variables.

I've noticed that sometimes the gas block is not perfectly aligned, and even a very tiny amount will translated to a slightly different gas tube alignment.
I've also noticed that gas tubes are not perfect either.
Tolerance stacking may be your problem.

Bending the gas tube a couple thousandths may just reduce your tolerance stacking enough that it will not cause problems with other BCGs.

Or you can start chasing the problem by replacing parts, which is time consuming and expensive. I would start with bending the gas tube.

[HeruMew]

Got some decent feedback here.

If you have a way to stake the gas key, replace it and try it out before staking them down.

Otherwise, I would hold the company accountable. Sent out once for warranty and returned with another, or the same, issue? Nah, refund or replace with new.

I wouldn't tweak my rifle or anything if the other carriers work in it. I do agree, it probably won't cause issues, but that's on the line of "Fixing something that's not broke." if every other carrier works except that one. Fix the broken part: The BCG. Not the upper.

[markm]

What method would you use to bend the gas tube?

The standard big flat head screw driver is what I've used. Not sure if that's the optimal solution in this case, but that's what I've been shown by the boss.

[bamashooter]

I'm thinking of doing one of these, but hoping to gain a little knowledge in the process. Of 4 uppers and three carriers, only one carrier doesn't work in every single upper.

What method would you use to bend the gas tube?

To avoid kinking, I've "heard" of filling the tube with sand (I've done the sand thing on other small tubing, soapy water (fill the tube, plug the ends, and freeze /soap allows bending without an immediate shattering of ice), and 3mm / 0.120" weed trimmer string. The ID of the tube is spec'd at .120". Assuming this will take a few attempts, I'd try string first followed by sand. You can also use anything like talcum powder. Cool video on frozen water method or you can start at the 3:28 mark. https://hackaday.com/2013/01/21/buil...l-metal-tubes/

Additionally, you can go to a hardware store, pick up a couple of small pulleys, wood screws, attach pulleys to a board and use that to assist you. You can probably use a couple of thread spools in place of the pulleys.

[opngrnd]

A couple notes on this project. I don't think bending the gas tube will be a complete fix, and possibly not a fix at all with the gas key being so finicky. Taking the rail off but leaving the barrel nut, I can flex the gas tube anyway I want through the front of the upper with my hand and I'm still bumping into the gas key to a degree I would be worried about damage to the gas tube or gas key while firing. In the gas tube's current resting state, I feel too much of a bump from the gas key while handcycling to be comfortable firing the weapon, and every other way I moved the gas tube seems to be worse. I'm hoping this helps narrow the problem to the gas key, so I added a BCM gas key onto a small order of parts I was doing and will replace the gas key. I'll see where that ends up leaving me, and look at what needs to happen concerning the gas tube after that. I've never replaced the gas key anyway, so it'll be interesting to do and may possibly fix the issue.