Troubleshooting TNA 7.5 upper

[Horilka]

Gentlemen, I'm trying to troubleshoot TNA 7.5" upper numerous issues (failure to extract, failure to strike the primer, feeding new round while spent case not ejected) and for the beginning was wandering about two things to stars with - gas tube and adjustable gas block.. I am thinking about either undergassed or overgassed and adjusting gas block doesn't change a lot...

1) As you can see gas tube is made of two pieces, I never heard about such gas tubes, is that some kind of hack or what? There's powder residue around, but it might be back from upper, tubes sit snug, not sure what to think.
2) upper has "field adjustable gas block" which honestly looks like a junk to me. Anyone can identify manufacturer so I can google some info on block? TNA could not identify what they put there...
For reference this is the upper I'm working with..

https://www.canadiangunnutz.com/forum/showthread.php/1599823-SOLD-OUT-Assembled-7-5-quot-Pistol-Uppers-limited-quantity


This is the gas tube:



And powder residue:



Gas block, I moved it from its place over the port.

 

[Stevo]

Bolt has good extractor and ejector?

Not hitting the primer probably indicates it's not in battery, as long as the firing pin isn't busted.

Does it lock open when you fire with one round in the gun and empty mag?

 

[Horilka]

Well, I put this upper on my M&P Sport II lower to test. Started with 4 or 5 mags with single round, cases were ejected 1-2 o'clock, bolt hold open every time. Then loaded 5 rounds in each mag and sarted getting issues I described in first post. I though it might be undergassed, increased gas with adjustment screw - 1, 2 up to 5 turns, no difference at all. I think 1 o'clock actually is a bit overgassed, while 2 o'clock is about right... anyway, I was keeping getting issues.
So I swapped whole BCG - from my Sport II. I was getting same results. As this stage I thought I need to take a pause and do proper inspection of gas block and inspect everything at home and do some thinking before hitting range next time and just wasting ammo.
This is how I found I have two-piece tube and gas block with adjustment screw that poorly held in place with spring detent.
So now I wonder is it normal to have two piece gas tube and which brand this gas block is. I'm planning to remove compensator to fully remove block and inspect it before putting back..
Then I'll look into possibilities of over/under gassing... and maybe bolt bouncing.

 

[JohnnyP636]

My friend bought a similar 7.5" kit from TNA that you have to assemble yourself but his barrel is raw stainless steel, I helped him assemble it and we had many issues.

First the gas tube was making contact with the barrel nut, forcing in into the upper at a upward angle not allowing the gas key to align with it properly. I had to bent that into position for the thing to even work

Then day one at the range it turned into a single action, would not cycle properly, bring it back home and the un staked gas key bolts were loose and the gas key almost fell off, torque them down and stake properly

Then back to the range and we then getting failure to eject, sometimes ripping the rim right off the cases. Bring it back and even though I torqued the barrel nut down properly the barrel got loose, it seemed as though the fit wasn't good and it didnt seat all the way even though the torque was reached. And only after being shot did the barrel seat into the upper properly. Because when we re torqued it, it took quite a bit more turning of the nut to reach the torque again.

Im not sure if he has been back to test it out since, but he learned his lesson already buying cheap kit

I dont believe your gas tube is 2 piece, its just been turned down in diameter where that step is. Its one tube

 

[Stevo]

Is that a lock screw on the receiver side of the gas block?

Can it be turned with the gas block installed?

 

[Horilka]

Then back to the range and we then getting failure to eject, sometimes ripping the rim right off the cases.

Thank you for sharing your experience, adjusting my expectations accordingly...
Now that you mentioned it, I recall another issue I had - it takes slamming the rifle while holding charging handle to eject chambered unfired round...

Is that a lock screw on the receiver side of the gas block?

Can it be turned with the gas block installed?

That is screw with spring detent inside. You can't turn it while gas block is in its place. In theory you should screw it in, and detent would stop adjustment screw from rotating (adjustment screw has one long notch along its length), but because of ####ty quality both screws a bit loose.

 

[JohnnyP636]

Thank you for sharing your experience, adjusting my expectations accordingly...
Now that you mentioned it, I recall another issue I had - it takes slamming the rifle while holding charging handle to eject chambered unfired round...


That is screw with spring detent inside. You can't turn it while gas block is in its place. In theory you should screw it in, and detent would stop adjustment screw from rotating (adjustment screw has one long notch along its length), but because of ####ty quality both screws a bit loose.

How good is the fit on the gas block? The one we had was not adjustable but it was a loose fit on the barrel journal, and I can see after many shots that it was also leaking as there was signs of blow out around it on the barrel

Also it looks like a set screw type? Was there a dimple for the set screws already drilled in the barrel for proper alignment? Ours was not and I drilled that myself using my drill jig. I have had some gas blocks that needed to be pushed on right up against the journal shoulder as far as possible to align with the gas port hole in the barrel. While on others there needed to be a slight gap for proper aliment

 

[Horilka]

How good is the fit on the gas block? The one we had was not adjustable but it was a loose fit on the barrel journal, and I can see after many shots that it was also leaking as there was signs of blow out around it on the barrel

Also it looks like a set screw type? Was there a dimple for the set screws already drilled in the barrel for proper alignment? Ours was not and I drilled that myself using my drill jig. I have had some gas blocks that needed to be pushed on right up against the journal shoulder as far as possible to align with the gas port hole in the barrel. While on others there needed to be a slight gap for proper aliment

Mechanically gas block fitting was good IMO, I still need to take measurements to see if it was aligned properly. But for that I would need to remove compensator, it seems to be tightened too much. Will get to my friend's big vice to do it. Set screw is of this type so no need to adjust it in theory