View Full Version : Severe gas leak
Anyone ever seen a gas-leak of this magnitude? Went as far back as the pivot-pin lug.
"Functional" Specs:
DD 10.3 barrel, A2 FH
Straight Pinned Vltor low pro GB -- Tightly set screwed prior to pinning.
BCM BCG -- no o-ring
BCM H2 buffer, spring and RE (Kit)
Ammo: M193
http://farm6.staticflickr.com/5524/9192328056_2ed5280fb4_b.jpg
Leak looked to be coming from the rear of the GB, right at the barrel's shoulder. There's about a credit-card-thick gap between the block and the shoulder, if that matters. No issues on semi-auto, locked back every time. He had a couple of Brass-Over-Bolt's on full auto, with the same buffer weight, which I attributed to cycling speed.
This question has been batted around and is often argued but is there supposed to be a gap between the gas block and shoulder with a Vltor gas block? I would think that if it were leaking from under the gas block, the gas would be deflected perpendicular to bore by the shoulder. That is to say it couldn't travel down the barrel as far as the receiver. Is there any chance it's leaking around the gas tube?
The bolt over base malfunction is a result of an unserviceable magazine and has nothing to do with bolt speed.
This question has been batted around and is often argued but is there supposed to be a gap between the gas block and shoulder with a Vltor gas block?
I've done quite a few vltor gas blocks and one BCM gas block with my BRDE dimple jig and even the jig is setup to leave a handguard cap thick gap between the shoulder and GB.
CC, how long has this rifle been built...or better question how many rounds through it before this started happening. Has it always done this or just began doing this? My old Daniel Defense carbine gas 16" rifle with vltor GB leaked liked like crazy from the gas tube yet functioned perfect. Half the barrel was brown. I suspect because of the rifle being a carbine gas 16" barrel it could afford to leak gas yet still be reliable.
-Jax
There doesnt have to be. The gas block in question used to be mine, for a build that i never got around to doing. It's been about 3 years but i know i verified it with a caliper.
I initially thought it was from the tube but he pointed to the block and shoulder having the same rust-color sprayed all over it. I suppose it's possible that it may have come from the tube. And, in retrospect, the fact that the tube wasn't too affected by the discoloration could mean it might have been the source of the leak.
The malf was a spent case wedged between the bolt and the upper-- a failure to eject**. Sorry, wrong terminology. I thought it was a bad ejector but he said it only happened in full auto. I also later verified the ejector to be 100% functional, hence, the reason i concluded it to be caused by a combination of bolt speed and premature extraction, thus, failing to completely extract the spent case and, in turn, failing to eject it.
I've done quite a few vltor gas blocks and one BCM gas block with my BRDE dimple jig and even the jig is setup to leave a handguard cap thick gap between the shoulder and GB.
CC, how long has this rifle been built...or better question how many rounds through it before this started happening. Has it always done this or just began doing this? My old Daniel Defense carbine gas 16" rifle with vltor GB leaked liked like crazy from the gas tube yet functioned perfect. Half the barrel was brown. I suspect because of the rifle being a carbine gas 16" barrel it could afford to leak gas yet still be reliable.
-Jax
Not long at all. Less that a thousand rounds young. It may have been an accumulation from the last two range trips but i think he only noticed it this last time. I agree that it being a CAR is one of the reasons it's able to get away with it. IMHO, it's also so over gassed, it resulted in the 2 FTEs, despite such a leak.
Do you think the gas tube may have a crack or some sort of perforation?
justin_247
07-02-13, 12:57
This may sound crazy, but maybe the gas is venting from the upper receiver gas tube port?
This may sound crazy, but maybe the gas is venting from the upper receiver gas tube port?
Have seen gas tubes get absolutely filthy right were it enters the upper but never THAT much. Don't take that wrong though man. Not dismissing your suggestion.
CC,
I suggest taking the Centurion rail off. Clean the upper and rail very well. Especially the gas tube and block. Reassemble and start shooting. Inspecting after each shot. In cases like this someone needs to invent a product similar to UV dye used in locating leaks in engines. ;)
-Jax
Thanks everyone! At this point, im not dismissing anything and will see about getting the gun back to give all mentioned possibilities a look. I'll definitely give the shooting-it-clean a shot. I think that's the only way to narrow down the source, short of using a high speed cam. :D
I'll update the thread when i figure it out.
Looking forward to seeing what you find out!
-Jax
This question has been batted around and is often argued but is there supposed to be a gap between the gas block and shoulder with a Vltor gas block?
The only gas block that is done right that I know of is the Noveske. Every other gas block I have seen just uses the same offset for the gas hole as a front sight, so they should be a handguard cap space from the shoulder.
The only gas block that is done right that I know of is the Noveske. Every other gas block I have seen just uses the same offset for the gas hole as a front sight, so they should be a handguard cap space from the shoulder.
Is the Noveske offset so that you can flush it up against the shoulder on the barrel?
^Just looked at mine and it is.
As for the vltor, to clarify my earlier post for anyone reading this down the road, the block's port is large enough that you dont have to leave a gap. You do, however, if want the ports dead-centered.
The only gas block that is done right that I know of is the Noveske. Every other gas block I have seen just uses the same offset for the gas hole as a front sight, so they should be a handguard cap space from the shoulder.
I'd argue that the Vltor gas block is done right also...
I just measured both a Noveske & Vltor gas block. The plenum diameter in both measured 0.162" (0.1615"+ Meyer Gage, NIST Traceable) and the center to back edge both measured 0.188". Admittedly, I used a set of electronic calipers but they are Mitutoyo Absolute Digimatics. I know two things at this point...
- The gas blocks are made by the same company, and
- It wasn't necessary for the OP's gas block to be pinned with a gap.
I measured the hand guard cap on a Colt 6920 at 22 gauge or 0.030" (0.0299" actual).
0.162 - 0.063 = 0.099 / 2 = 0.0495 or 0.050 per side rounded
If we offset the two holes by 0.030 that leaves approximately 0.020" before we would see any axial occlusion of the gas port on the OP's rifle.
http://i1363.photobucket.com/albums/r704/BallistaSystems/OFFICE-PC/th_P7020010_zps1d797c45.jpg (http://s1363.photobucket.com/user/BallistaSystems/media/OFFICE-PC/P7020010_zps1d797c45.jpg.html)
You can ID the Noveske gas blocks with the correct offset to install to the shoulder by the chamfer on the lower front of the gas block. It is cut at a radius following the round part of the gas block, not flat and straight across. It would measure around .215" to the pin.
I was not saying there is anything wrong with other gas blocks, just that they are not correct to install to the shoulder. You can get away installing one to the shoulder on a 14.5-16" carbine but the room for error goes down the bigger the port gets. It also goes down faster the more misaligned they are.
sinlessorrow
07-05-13, 01:05
Ok I am going to ask the dumb question, what oil do you use and any chance it got on the rail?
Not my gun but last I checked, he was using froglube. Let me verify when I see him this weekend. Are you looking at the possibility lube may have gotten on the rail and burnt off, leaving that residue? It didn't appear to be so. It looked sprayed on. I told him to look on the bright side... At least, he now has the SOCOM DE rail he's always wanted. :lol:
This thread is almost a year old but the guy finally showed up to our group shoot again. Confirmed. Like Jax's, it's leaking at the block, from the gas tube. He's been shooting without us and it's sealed up quite a bit on its own. He also bumped up to an H3 and solved his extraction issues.
This thread is almost a year old but the guy finally showed up to our group shoot again. Confirmed. Like Jax's, it's leaking at the block, from the gas tube. He's been shooting without us and it's sealed up quite a bit on its own. He also bumped up to an H3 and solved his extraction issues.
Do you think the issue was that the hole for the gas tube was bored too large or was there a sloppy fit to the barrel?
I wonder who put the gun together. You can feel for what you're asking about when you do the assembly. But if it's only your first or second gun, you don't notice oddball stuff like that.
Ha! I almost did. He swung by my place to have his barrel nut torqued. To be honest, though, I've built maybe 3 uppers and I dont know if it would occur to me that the fit was off.
mtdawg169, I assume the tube hole was bored a tad large. It wasn't at all loose when I tried it on my former barrel it was originally intended for.
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