Gas tube to Gas key

[KeepnitReel]

Hey NWFA, Anyone have any experience with a gas tube being to loose in the gas key? I'm having a weird short stroking/stovepiping issues with my 6.5 Grendel lefty. I run adjustable gas blocks, good gas tubes, and quality BCG . Well this is my first experience with BlackRain as they are one of the only companies that build a NiB lefty BCG. Quality of the BCG looks very nice, but when checking the double flare gas tube into the gas key, it seems to be loose,,,,,,, compared to all my others.

Specs since I know I will be asked.

20" underground 6.5 Grendel rifle length gas
Matching lefty Underground bolt to barrel
Blackrain NiB carrier.
Blackrain billet lefty upper
Odin adjustable SS gas block and SS rifle length tube.
Using hornady amax factory match ammo.


All the specs show it should be operating correctly. Gas rings are perfect, alignment of gas block is perfect, no signs of carbon from leaking. Gas key is extremely tight and show no signs of leakage. Bolt is locking correctly and the only thing I can't check is dwell time on pressures. I've tried everything from heavy buffer weights to a empty 1.9 oz buffer weight with zero differences in results.
The only thing that seems to be sticking in my head is how loose the flare on the gas tube is in the gas key.

I always measure gas port alignment on the barrel to align gas block to port, since they are never all the same. Don't think that nice little lip of the barrel is where the gas block should be pressed up against, all of mine are usually a business card or two of thickness off the barrel lip.

Anyways, looking forward to getting a fresh set of eyes and ideas on this. Thanks NWFA

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[v0lcom13sn0w]

is the gas port in the barrel obstructed? or too small? i had to drill one out in a 5.56 18" barrel with rifle gas system once

 

[KeepnitReel]

That's the first thing I thought but kinda the last thing I wanted to do. I have checked the hole diameter on barrel and it is in spec, have tested flow through the barrel by closing off the chamber and checking for leaks, nothing. I also use compressed air to check the BCG function, flawless on bolt locking and unlocking. The gas tube to gas key is the only thing that's waving flags at me. Seems like a really loose fit into the key. I could put more of a flare on it, but wanted to get some fresh eyes on it before I do anymore.

Does anyone have specs on how far the gas tube should be seating inside the gas key. Maybe length? All I know if I'm frustrated and my father will be here this Saturday and would really like to surprise him for his birthday with this rifle.

is the gas port in the barrel obstructed? or too small? i had to drill one out in a 5.56 18" barrel with rifle gas system once

 

[v0lcom13sn0w]

i have had ONE too long rifle gas tube and the bolt wouldnt go into battery. it was from raineer.

here's my thread with similar issue

AR15 Build issue. gas?

 

[v0lcom13sn0w]

see post #14

YMMV. just lettin ya know what solved my mystery

 

[KeepnitReel]

I think you are correct, and with the adjustable gas block I will be able to tune it "down" if needed. I'm going to get the slow-mo camera hooked up to see real time footage of the BCG. I'm getting ejections, just not bolt lock or feeding of the next round. I also have another mag coming to try different ramp angles. Thank you @v0lcom13sn0w

 

[v0lcom13sn0w]

I think you are correct, and with the adjustable gas block I will be able to tune it "down" if needed. I'm going to get the slow-mo camera hooked up to see real time footage of the BCG. I'm getting ejections, just not bolt lock or feeding of the next round. I also have another mag coming to try different ramp angles. Thank you @v0lcom13sn0w

not sure if i mentioned it but when i drilled out the port i put a cleaning rod with a brush on the end down the barrel before drilling to protect the rifling and also to remove any shavings from drilling

 

[v0lcom13sn0w]

also, do you have access to another BCG to try? i skimmed thru your other posts again and didnt see anything (i think)about trying another bcg

 

[KeepnitReel]

I would do that in a heart beat , but it's a lefty!!! Ugh.......

also, do you have access to another BCG to try? i skimmed thru your other posts again and didnt see anything (i think)about trying another bcg

 

[Medic!]

see post #14

YMMV. just lettin ya know what solved my mystery

Then it sounds like post #15 would apply again, again.

 

[v0lcom13sn0w]

I would do that in a heart beat , but it's a lefty!!! Ugh.......

maybe could take some compressed air and soapy water to leak check around the gas key? just try exhausting all options before drilling.

 

[KeepnitReel]

I was going to use compressed air while drilling to blow anything out the end. But I'll keep that in mind as well. I did just flange the gas tube end a tiny bit more. Getting much better seating now inside the gas key and still getting a smoothly locking into battery with the 45 degree slide test...

not sure if i mentioned it but when i drilled out the port i put a cleaning rod with a brush on the end down the barrel before drilling to protect the rifling and also to remove any shavings from drilling

 

[v0lcom13sn0w]

Then it sounds like post #15 would apply again, again.

 

[HB of CJ]

Wow. Any way you can swap gas tubes and carrier keys? Consider high temp sealing compound instead of staking the key? Is the gas tube physically long enough? Is the "flair", (never heard it called that) of the gas key considered OEM spec?

Adjustable gas blocks. I am not fully familiar with them. Is the max gas adjustment setting working correctly? Do you have any spec info from the gas block manufacture regarding percentages of gas flow at various restricted settings? Max setting?

Last thing to consider which you already covered. We must "assume" the gas port diameter in the barrel is correct. Perfect alignment of the gas tube gas hole, the block and the barrel gas port hole is vital. Even a little bit off restricts high speed gas flow.

Other than that I am stumped. Can you mount an OEM front site/gas block assembly and test? I am assuming you have no OEM taper pin slots in the barrel. Right now I am thinking gas tube length and possible gas block restrictions. Yikes.

Long shot. Are you running a OEM spec RIFLE butt stock type buffer and spring group? Does the bolt carrier group manually retract back fully? Does the bolt carrier reach back far enough to fully engage the bolt stop group? Some incompatibility?

Could be a combo of several things. Assuming full power ammo? I am interested in how this pans out because right now I also want to build that last ride left hand 20" HB Rifle 6.5 Grendel. This may be beyond my experience level. Sorry.

I am stumped here. Yikes again. Hundreds of AR15 builds. Getting too old.

 

[v0lcom13sn0w]

btw i just remembered some adjustable gas blocks have a "bleed off" setting when the set screw is all the way open. when "all the way open" is actually like 3 turns counter clockwise from all the way closed. confusing, i know but i remember reading instructions on one gas block that had that feature. might wanna double check your gas block instructions

 

[KeepnitReel]

Ya that's not the style gas block I use. But I have seen those..

btw i just remembered some adjustable gas blocks have a "bleed off" setting when the set screw is all the way open. when "all the way open" is actually like 3 turns counter clockwise from all the way closed. confusing, i know but i remember reading instructions on one gas block that had that feature. might wanna double check your gas block instructions

 

[KeepnitReel]

Rifle length buffer tube and buffer weight is almost identical, just add the extended buffer length to make up the difference. Thank you for your thoughts on this. I waiting for Jason from underground to get back to me on gas hole diameter, but I'm thinking the hole diameter is the issue.. the Grendel actually puts out less gas pressures then the 5.56/223.. good to know.

Wow. Any way you can swap gas tubes and carrier keys? Consider high temp sealing compound instead of staking the key? Is the gas tube physically long enough? Is the "flair", (never heard it called that) of the gas key considered OEM spec?

Adjustable gas blocks. I am not fully familiar with them. Is the max gas adjustment setting working correctly? Do you have any spec info from the gas block manufacture regarding percentages of gas flow at various restricted settings? Max setting?

Last thing to consider which you already covered. We must "assume" the gas port diameter in the barrel is correct. Perfect alignment of the gas tube gas hole, the block and the barrel gas port hole is vital. Even a little bit off restricts high speed gas flow.

Other than that I am stumped. Can you mount an OEM front site/gas block assembly and test? I am assuming you have no OEM taper pin slots in the barrel. Right now I am thinking gas tube length and possible gas block restrictions. Yikes.

Long shot. Are you running a OEM spec RIFLE butt stock type buffer and spring group? Does the bolt carrier group manually retract back fully? Does the bolt carrier reach back far enough to fully engage the bolt stop group? Some incompatibility?

Could be a combo of several things. Assuming full power ammo? I am interested in how this pans out because right now I also want to build that last ride left hand 20" HB Rifle 6.5 Grendel. This may be beyond my experience level. Sorry.

I am stumped here. Yikes again. Hundreds of AR15 builds. Getting too old.

 

[HB of CJ]

Thank you. I need to learn more about the 6.5 Grendel. Also it may be a bummer being Left Handed. I am. Yikes!