Am I looking at a gas block problem?

[BocaDan]

Hi Folks,

I'm trying to troubleshoot a no-name 16" mid length upper. Every so often the bolt does not hold back after last round. Also I'd say every 20-30 shots the firearm cycles ok (spent case ejects), click, no bang, and there is no cartridge in the chamber. I've played with buffers, tried different ammo, bolt, entire lowers and magazines.

Do the pictures mean anything? I am assuming (very novicely) that the gas block is somehow not in spec and is leaking gas and/or was not installed properly...

2nd picture is the same as the 1st, but I suspect there is gas leaking in the highlighted area? I am not technical savvy to decipher them. Also does the gas port look ok?

Thanks in advance...

[SomeOtherGuy]

I see nothing obviously wrong with the gas port. The carbon fouling almost centered around the port is a good sign because it indicates that the hole on the gas block is completely over the port.

I know you said you had tried different ammo and magazines, but what specific ammo and magazines have you tried?

What does the gas block itself look like? Is it a sight tower block and pinned, or low profile? What does the gas tube look like? Have you looked for any damage, cracks or holes in the gas tube?

[BocaDan]

In addition to my post above, the gas tube is covered in dark sooth. Is the only way it can get that dark is gas coming back from here (see below pic)? Or am I really looking at a bad/leaky gas system here?

[BocaDan]

I see nothing obviously wrong with the gas port. The carbon fouling almost centered around the port is a good sign because it indicates that the hole on the gas block is completely over the port.

I know you said you had tried different ammo and magazines, but what specific ammo and magazines have you tried?

What does the gas block itself look like? Is it a sight tower block and pinned, or low profile? What does the gas tube look like? Have you looked for any damage, cracks or holes in the gas tube?

Thanks SomeOtherGuy. I tried HK, Magpul and lancer mags. The Magpul is gen 2 & 3 mixed. Ammo is tula, brown bear and American Eagle... The gas block is low profile, not pinned but is the screw to the barrel (dimple) type. Here is a pic of where its screws meet the barrel (not too deep)... You can see the gas tube too...

[BocaDan]

Have you looked for any damage, cracks or holes in the gas tube?

That's good idea & starting point... Thanks!

[Edgethane]

From your description, the gun is appears to be getting just enough gas to work, most of the time.

Doesn't look like the gun is losing gas from the port, all the barrels I've ever seen look just like that.

There is some gas loss from where the gas tube enters the block. Sometimes, this resolves when the gas tube gets enough fouling around it to seal off.

Your gas port could be too small, but I think that's on the less likely end of probability. It's more likely that the gas block was drilled out too large where the tube enters.

How easy was it to remove the gas tube from the gas block?

[Edgethane]

Oh, just saw the added pictures.

Too, too much fouling around that gas tube.

What's that 'step', just to the right of center picture, on the gas tube?

[556BlackRifle]

Oh, just saw the added pictures.

Too, too much fouling around that gas tube.

What's that 'step', just to the right of center picture, on the gas tube?

Yeah, I'm wondering the same thing.

[SomeOtherGuy]

Thanks SomeOtherGuy. I tried HK, Magpul and lancer mags. The Magpul is gen 2 & 3 mixed. Ammo is tula, brown bear and American Eagle... The gas block is low profile, not pinned but is the screw to the barrel (dimple) type. Here is a pic of where its screws meet the barrel (not too deep)... You can see the gas tube too...

Something looks wrong with the gas tube. They would normally have a little soot at each end, but not much (or zero) in between. I would inspect the tube closely and also look at its fit within the gas block. If you have access to a new gas tube, I might just replace it as the next thing to try. They don't cost much. But if the gas block is too loose around the tube, that could be a problem also. I suspect your problem is either the gas tube or the fit of the tube into the gas block.

Has this gun been abused, used for repeated mag dumps or that sort of thing? Or maybe the gas tube got hit or bent somehow?

FYI, Tula ammo is reputed to be fairly poor. However, Brown Bear and American Eagle should be OK. Pmags and Lancers usually work fine, so it sounds unlikely that magazines are the problem.

[Kokopelli]

I would try a new tube for sure.. Cheap and then you could rule out the tube.. Gas block next.. JMO