Gas Length Problem

[tlw613sp]

I started building a new upper and am having an issue with the gas tube. It is protruding too far into the upper, preventing the BCG from going all the way forward. I tried 2 separate BCG's from known working rifles to check.
I double-checked the roll pin is in the correct position (not in front of the tube). I took a few measurements and was hoping someone could measure some of their parts to confirm if something is obviously out of spec.

This is a carbine length gas system.
Gas tube is 248.5mm long and 243.5mm from center of roll pin hole to BCG end.
Rear of barrel extension to rear of gas block is 199mm.
Rear of gas block to center of gas block's roll pin hole is 17mm.
Gas block OD at rear is 4.59mm.

Other notes:
Barrel was pre-drilled for a gas block roll pin. The gas block is seated against the barrel's shoulder and pinned in the pre-drilled spot. This appears to be in the correct position.
I removed the roll pin and put the BCG in the rifle. I pushed the gas tube as far back as it would go, and the tube's roll pin hole is still forward of the gas block's roll pin hole.

I don't have another carbine length rifle to measure against, my others are pistol and midlength. If someone with a carbine system could measure, that would be great!
If I'm missing something obvious, please let me know as well.

*EDIT* I have spoken to both the retailer and the manufacturer. The retailer was great and took some measurements of his stock of the same parts. His and mine matched. I am still awaiting resolution from the manufacturer.

*UPDATE* The manufacturer requested the upper to look at and I sent it to them. They dropped a BCG in and it test fired fine. They sent it back to me. While they had the upper, I bought a new BCG. When I received the upper back, the new BCG dropped right in. The other 2 BCGs from the other rifles still don't work. I'm not sure why those don't work, but I now have a working rifle with the new BCG, so I guess I'm good now.

[TomMcC]

When you say it's protruding too far into the upper receiver, did you, as a rough visual, compare it to your other guns? And the tube is straight, right? Not canted to one side? Also, there is nothing in the receiver where the gas key telescopes unto the gas tube and sorta of into the receiver? One more thing, the hole in the receiver where gas key telescopes in is the proper diameter?

[tlw613sp]

When you say it's protruding too far into the upper receiver, did you, as a rough visual, compare it to your other guns? And the tube is straight, right? Not canted to one side? Also, there is nothing in the receiver where the gas key telescopes unto the gas tube and sorta of into the receiver? One more thing, the hole in the receiver where gas key telescopes in is the proper diameter?

I left out one dimension. The gas tube protrudes 27.5mm from the barrel extension. My other 2 uppers are 24mm & 25mm. It is visually further into the upper than my others. The cam pin cutout is an easy reference point to see it clearly (the measurements confirm it).
The gas tube telescopes inside the carrier key without resistance until it hits a hard stop at the very end. The tube is straight and while there is a slight bit of play where the tube enters the upper, I don't perceive that to be an issue.

[TomMcC]

MMMMM??? What's the measurement from the back of the gas block to the face of the receiver? I have a carbine length gun and that dimension would probably the easiest for me to measure.

[tlw613sp]

MMMMM??? What's the measurement from the back of the gas block to the face of the receiver? I have a carbine length gun and that dimension would probably the easiest for me to measure.

185mm. Maybe a hair over.

[TomMcC]

185mm. Maybe a hair over.

Just measured mine. It has an stock A frame front sight with the stock hand guard holder....it's 187mm. So on your gun the tube protrudes 2.5 mm. You sure the gas block is supposed to be seated on the shoulder with that barrel?

[1_click_off]

Do the gas keys in the 2 BCG that don’t work have a carbon buildup in them preventing the gas tube from entering the key fully?

[tlw613sp]

Read your update. IMO something is still wacked with that upper. You should be able to put any reasonably well built BCG into any reasonably well built upper. Is the gas tube still protruding into the upper farther than some other uppers you've inspected? I did a quick measure comparison of 4 gas keys and they were all different internally to the internal shelf. They were all within about an 1/8" of each other. I could interchange them all.

Yeah it still protrudes farther than the others. This one is about 3/4 of the way to the rear of the cutout.

Do the gas keys in the 2 BCG that don’t work have a carbon buildup in them preventing the gas tube from entering the key fully?

This was my first thought. I don't really have a good way to clean them out. I tried a .22 bronze brush but it was stiff and felt like it would get stuck.