Gas tube leak by?

[wyrmzr]

165368
I just noticed this on my bull barrel for my AR. My 300 AAC barrel doesn't seem to have this same leak by at the gas tube/gas block juncture.
The rifle functions fine, the gas tube is clear, but I was mostly just curious as to whether this may be something to be concerned about?

[Adam Helmer]

wyrmzr,

It seems you have an arm with the direct gas impingement system. I own several, but prefer Piston Driven arms. Only the M1942 Swedish Ljungman, U.S. M16 and the Egyptian Hakim have used the direct gas impingement system. I see many current ARs are piston driven. That is a improvement, in my humble opinion. I was issued an M16 in July 1965. I did not like the gas system then and still do not.

Adam

[Mk42gunner]

I'm no expert when it comes to building AR's, but it appears to me that your gas block doesn't fit your barrel correctly.

In the thousands of M16's that I owned (Armorer in a Seabee battalion) I never saw gas leakage at the juncture of barrel and gas block.

Robert

[country gent]

As long as the rifle is functioning reliably the leak is not a big problem. Just to remeber to clean it every so often. The tube can be sealed of by removing it from the block and a little clear gasket material spread around it and in the hole then reassembled and allowed to cure. The area and small gap this holds for quite awhile if the leaks bothers you. I made some gas blocks that clamped the tube in place rather than pinned it. when the 6 4-40 screws were tightened up it sealed up really good.

[wyrmzr]

I was actually wondering whether this wasn't just a slightly out of spec tube or gas block; it is pinned in place, and when running H335 behind 55 grain FMJBT bullets, the lowest recommended load of around 25.4 grains of powder functions flawlessly. Any more powder than that, and all I get is a fireball, with the same point of impact.
I'll keep it clean, and maybe eventually upgrade to a clamp in tube just to make sure I'm not wasting energy (and therefore powder).
As far as going piston driven, I'm not yet sold on it because of my overall results.
And finally, the leak is not between the gas block and barrel, but between the gas block and gas tube. If it was at the barrel, I'd assume a bad alignment, but I seem to have no issues with it leaking there.

[lefty o]

i little bit is not abnormal, but that is severely excessive.

[wyrmzr]

I'm wondering if the excessive powder isn't just the result of my running some hot loads while working up loads for this barrel; behind 55 grain FMJBT bullets, the H335 functions fine with 21.5 grains of powder, but I decided to try and step it up anyway.
The end result of pushing up to 22.8 grains of powder left me with the same point of impact, but a 2 foot long, 6 inch diameter fireball exiting the barrel. That much wasted powder may have blown by the gas tube and created the mess I ended up with.
It was fun to watch the fireball, but of course it's not efficient, as it means I'm burning powder outside the barrel, and probably just creating unnecessary pressure in the chamber.

[Gtek]

Just commenting on a dark little picture. Looks to me there is no fowling around gas port hole, this tells me block to barrel fit is good. It appears to be a tube in block issue, hole ID or tube OD issue. That amount of "leakage" seems a little over the top to me. Push roll pin and if tube wiggles in block?

[wyrmzr]

The tube seems to be tight in place, but I may pick up an extra gas block/tube combo just for the sake of 1) having a spare and 2) trying them out to see if I get less blow-by.
It wouldn't hurt to have some spare parts around anyway, given the current political climate.

[Gtek]

Tube in place with roll pin in or removed?

[wyrmzr]

With it in.

[Gtek]

Well, what does it feel like with the pin out? The pin may just have it rigid in block, back to OD/ID thing.

[wyrmzr]

I kind of loathe the idea of pulling the pin out right now, but that's because I'm mostly using the 300 AAC upper anyway, and in the off chance I switch back to the 5.56/223 upper, it functions OK.
I'll wind up pulling it before long, but I'm not sure exactly how long that will be. As I've said, it may be a good idea to stock up on parts for my AR builds before election time comes around.
Perhaps an 80% lower or two should be in the works as well.... I do know a machinist who can help me complete those.