gas tube question

[hoopharted]

so im going to be replacing the gas block on a new rifle when it gets here to one with a picatinny rail for iron sights , ive watched a couple vids , im curious about the gas tube , it appears to just sit in the block , how does it seal to keep pressure from bleeding off , at either end , thanks in advance

[Inkslinger]

It’s held in with a roll pin. Is does have a minuet amounting gas leakage in the beginning, but carbon buildup quickly seals it off.

[hoopharted]

thats wild ,seems sorta in efficient , thanks for the reply , and explanation

[Clint]

The other part of the answer is the fit between the gas tube and gas block hole is designed to be very close, so minimal leakage should occur.

The tube itself has a plug crimped into the forward end to seal it in that direction.

[Inkslinger]

thats wild ,seems sorta in efficient , thanks for the reply , and explanation

The amount of gas pressure going through the tube is very high. Some small amount of gas escaping from a very tiny gap at the gas block hasn’t seem to be of any detriment to a rifle that’s been in service for a very long time.

[DwayneZ]

Here's my 2cents on this.

1cent - it is most important to make sure the block is aligned to the port in barrel. It is not trivial ez to align the ports. After my 1st misalignment (verified with a bore scope) I made myself a wooden dowel jig where I can use my own sized wooden pins to make the alignment.

2cent - some gas blocks have the tube hole drilled all the way through, others do not. For the blocks that are not through hole you can seat the tube until you see the pin alignment, then back the tube out ~1/8", add a smear of silicone on the tube right at the block face, then gently do a 360 turn on the tube while pushing it back in to align the pin and then pin it in place. For through hole blocks, align the pin hole and with a fine point sharpie put a line on the tube right at the block face, then push the tube fwd (bore fwd) until the capped end of the tube sticks out about 1/8", add a smear around the tube, then slowly do a 360 of the tube while pulling is back, pull back until you see the line/mark you made, pull another 1/8", add a smear, 360 it back into place, pin it. You can then plug the fwd end of the block with silicone if you want to (if there is a recess, etc). I use long pins on the blocks as I don't care they stick out some, but on the short pins that end up flush, just finger smear silicone over the ends of the pin. Wipe off any excess, etc.

If ever you need to disassemble it all, silicone will not stop that process.

Is it needed? No. Does it make a seal that "prevents" gas leaking, yes. But as others have said, burnt powder residue will eventually clog up the small spaces there.

[1168]

1) It’s super easy to align gas ports. I use a BRDE dimpling jig.

2) There is no need to apply silicone. None. All risk; no benefit.

[utahjeepr]

1) It’s super easy to align gas ports. I use a BRDE dimpling jig.

2) There is no need to apply silicone. None. All risk; no benefit.

^^^ This! ^^^

The circumference area around the gas tube is something of a low (er) pressure "eddy", and hot carbon deposits there pretty quickly. The carbon deposits adhere much better than any silicone, and I can't imagine that any silicone placed isn't getting blown out of there as opposed to sealing the tube. This is a zero issue item, let it go.

[DwayneZ]

1) It’s super easy to align gas ports. I use a BRDE dimpling jig.

2) There is no need to apply silicone. None. All risk; no benefit.

Not all blocks have those type of set screws.
What risks? I have done silicone on a few builds, have not seen any issues after a few thou rnds each.
It doesn't "blow" out. All it does is help provide a better seal.

But agreed, no functional need to seal the gas tube.

[JoshNC]

Are we seriously giving credence to putting silicone sealant around the gas tube?