the gas key on my .224 valkyrie bcg is getting hung up on the gas tube and its making the action run really choppy. I took it apart today and checked the gas block to make sure the set screws were aligned with the dimple and they were perfect. I even switched gas tubes and it's still doing the same thing. could the barrel dimple alignment be out of spec? it's a 20" Wilson Combat in a LaRue UU kit.
Gas tube misalignment issues... Help!
- Thread starter AndrewO
- Start date
Barrel nut not aligned properly would be my guess, the hole in the nut can push the gas tube to one side if not perfectly aligned with the gas tube hole in the upper reciever.
I took the bolt, firing pin and cam pin out of the 6.8 carrier and tried it in my 5.56 and it didn't get hung up at all. I'm stumped haha.
there is a big space between the gas tube and barrel nut in the Larue upper kits. you don't need to time them or anything.
I gotcha, in that case just do what they taught us in the military, adjust (as in bend, gently) the gas tube in the upper until it stops hitting the gas key.
Gas key out of spec? I’ve got a BCG right now with that issue. Debating on sending it back or replacing myself.
If you get a gas tube alignment tool and simply set the gas tube so that it does not touch. Use a JP or other AGB with clamp retention. Then you are not locked in by the dimples in the barrel. You could also field mod the dimples to move your present tube over with a drill bit. If it's not free floating you are not going to get good accuracy anyway.
Have you tried another carrier in the 224vak? Maybe swap your 6.8 bolt into a carrier that you know has a good gas key and this will tell you if it's the gas key on your 6.8 carrier. Let us know what you find if you would?
Ok, my bad i see now that you already tried that. Pretty weird that it's happening with 2 different gas tubes. Either alignment or I guess the gas tube opening in the upper could be off? Hope you get it straightened out.
Ok, my bad i see now that you already tried that. Pretty weird that it's happening with 2 different gas tubes. Either alignment or I guess the gas tube opening in the upper could be off? Hope you get it straightened out.
I had a big name upper once that was over sized where the BCG rides. I could rock the BCG left and right in the upper enough that it would clip the gas tube. It took me 2 gas tubes being destroyed before I figured it out. Swapped uppers and no more slop. The BCG was a young match BCG which are oversized to begin with.
Can you elaborate a bit more? Do you mean that the gas key is hanging up on the gas tube a bit?
It seems like that is what you are saying (the test is to remove bolt and drop BCG into upper and it catches without going smoothly to full battery). If you see or feel any deflection while slowly feeding into battery, it needs to be tuned.
Of as described above, I had a bit of an issue with this in my Valkyrie which I promptly fixed by *very slightly* bending gas tube with small flathead screw driver to get it to ride smoothly on to gas key.
If that doesn't solve it, you could simply run fine grit snad paper around the tip of the tube at the flare to reduce the OD slightly and continue tuning. I have a few different BCGs and all of them run ever so slightly differently on the same tube.
Edit: just saw @JimLee posted similar fix.
Agree, could definitely be the gas key, or stacking of tolerances between key and gas tube. Seen it quite a few times. Typically I will take a little off the diameter of the gas tube where it meets the key.
I take it then that the key and the tube should never touch, right?
Is there a tolerance in thousandths that the gas tube needs to be away from the key?
Is there a tolerance in thousandths that the gas tube needs to be away from the key?
Not sure your going to be able to accurately measure for clearance, but you can measure for potential interference. As long as gas tube is .001" smaller in diameter than gas key inner diameter you should be good to go. Calpiers can check OD of gas tube but you'd really need pin gauges to check the gas key precisely. Calipers don't do that well for small ID measurements.
Tuning gas tube/key alignment is a feel thing (in my experience) and while tube may be clear of upper, it may need a slight adjustment to easily mate with gas key without binding.
