BCG technical spec question?

[ScottsBad]

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.

OMG as my teenagers would say. All you have to do is use something to push it down or pull it up. Or possibly, push it from side to side. This has worked for me at least twice that I can remember. You don't have to remove it or anything.

I'm having a hard time imaging that anyone would need to put that much effort into it. I just bend it, and then if its too much or not enough I bend it again.

[bamashooter]

OMG as my teenagers would say. All you have to do is use something to push it down or pull it up. Or possibly, push it from side to side. This has worked for me at least twice that I can remember. You don't have to remove it or anything.

I'm having a hard time imaging that anyone would need to put that much effort into it. I just bend it, and then if its too much or not enough I bend it again.

Having never had the need to bend this spec of tubing, I was offering possible solutions to minimize kinking. weakening the tube, etc. Perhaps it maintains its shape and integrity regardless; doubt it. If the problem exists only with the one key/ carrier, I'd replace those. Doesn't take much to either prematurely diminish the tube or to "despec" the functionlity of the firearm based on pressures, flow, volume, etc.

[bamashooter]

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.

So you asked the tube bending question before having this epifany?

[lysander]

The distance from the centerline of the bolt to the centerline of the hole for the gas key should be 0.781 inch.

The distance from the centerine of the long part of the gas tube to the reduced OD part of the gas tube should be 0.156 inch, and the two sections of the gas tube should be parallel.

Take a few measurements and find out which part is non-conforming.

[opngrnd]

So you asked the tube bending question before having this epifany?

I asked the tube bending question between finding a problem and then figuring out the problem may be more specific than I thought. I'm crawling rather than trying to sprint through this build. After seeing the gas tube might fix things, I fiddled with the gas tube alignment to figure out it's specific effect in the alignment with the carrier I'm trying to use. Doesn't appear to be the answer. I found the video you shared pretty neat.

[opngrnd]

The distance from the centerline of the bolt to the centerline of the hole for the gas key should be 0.781 inch.

The distance from the centerine of the long part of the gas tube to the reduced OD part of the gas tube should be 0.156 inch, and the two sections of the gas tube should be parallel.

Take a few measurements and find out which part is non-conforming.

Thanks for this. Look like I'll be doing a little math.

[AKDoug]

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.

I think we might have had the same boss. Anyhow, I see where Clint's concern is, but I haven't experienced it. Most of the time when I "tune" a gas tube it ends up working just fine with my other BCG's. I guess that is because I haven't come across an out of spec BCG, but I have come across several gas tubes that didn't line up when building an upper.

[opngrnd]

I think we might have had the same boss. Anyhow, I see where Clint's concern is, but I haven't experienced it. Most of the time when I "tune" a gas tube it ends up working just fine with my other BCG's. I guess that is because I haven't come across an out of spec BCG, but I have come across several gas tubes that didn't line up when building an upper.

That's just the thing for me. I've done between 10 and 15 uppers and I've never had an issue before, so I started this thread. I figure it's a great learning opportunity for me concerning innerworkings of the system that I've never given thought to before.

[bamashooter]

I asked the tube bending question between finding a problem and then figuring out the problem may be more specific than I thought. I'm crawling rather than trying to sprint through this build. After seeing the gas tube might fix things, I fiddled with the gas tube alignment to figure out it's specific effect in the alignment with the carrier I'm trying to use. Doesn't appear to be the answer. I found the video you shared pretty neat.

Good deal.

[bamashooter]

The distance from the centerline of the bolt to the centerline of the hole for the gas key should be 0.781 inch.

The distance from the centerine of the long part of the gas tube to the reduced OD part of the gas tube should be 0.156 inch, and the two sections of the gas tube should be parallel.

Take a few measurements and find out which part is non-conforming.

Not that I'm doubting you; do you have a schematic / engineer drawing depicting the measurements or another source? I ask only because I like to build reference libraries. Looked forever for his request and the only data I found is what appeared to be a "to scale" drawing which included no measurements. Could have set up a proportion but got lazy. Thanks.