6mm arc gas gun bolt lock back

[.7mm.]

Built a new 6 arc gas gun, using a aero adjustable gas block. The bolt won't cycle and lock back on an empty mag after firing.

Gas block is adjusted all the way open.
It will lock back by hand so its not a mag issue.
Its gotta be either a buffer weight or under gassed?

What are the usual suspects and recommended course of action?

 

[338 dude]

Built a new 6 arc gas gun, using a aero adjustable gas block. The bolt won't cycle and lock back on an empty mag after firing.

Gas block is adjusted all the way open.
It will lock back by hand so its not a mag issue.
Its gotta be either a buffer weight or under gassed?

What are the usual suspects and recommended course of action?

Is the gas block misaligned with the gas hole in your barrel? Is your gas tube blocked up? Is your load too light, what is your load?

 

[338 dude]

My loads are ran suppressed. If you are not suppressed you may not have as much pressure either.

 

[.7mm.]

Is the gas block misaligned with the gas hole in your barrel? Is your gas tube blocked up? Is your load too light, what is your load?

It might be misaligned, I havent checked yet.

I dont think its the load. Currently in load development but loaded up some middle of the road powder charge with 90 gr TGK's. 26.5 gr of XBR. 2600ish fps.

 

[338 dude]

It might be misaligned, I havent checked yet.

I dont think its the load. Currently in load development but loaded up some middle of the road powder charge with 90 gr TGK's. 26.5 gr of XBR. 2600ish fps.

My block is an aero precision, same as yours so that is not the problem, unless it is misaligned. here is a little load data from Hornady for your weight bullet.

 

[338 dude]

What buffer do you have installed? I went with an H2 weight buffer , and could've went with an H3

 

[ARlife4me]

Try and check hole alignment with a borescope? Also look down the tube and see if it's straight or cocked to 1 side? If cocked it'll cause drag on the bcg. Another way to check that is don't let the bcg close by spring force. Tou can either open the receiver and do a bolt function test by hand (stick your pinky in the carrier and pull slightly open and then close by pushing from the ejection port. Also with the bcg back, check the tube and see if it's in the middle of the handle track/slot. Some gas blocks won't be pushed up against the journal shoulder for block and gas port alignments. This is due to either block dimensions or when gas port is reamed after being headspaced. I use (sometimes) AP blocks (adjustable and non), but don't know the port size in the blocks?

 

[338 dude]

JP - Buffer Springs and Silent Captured Springs

 

[.7mm.]

My block is an aero precision, same as yours so that is not the problem, unless it is misaligned. here is a little load data from Hornady for your weight bullet.View attachment 526061

The 90 grain gmx isn't really a good comparible bullet to use as a starting point for load data on 90 grain TGK's.

Because of the difference in length from a 90 grain mono metal and 90 grain lead core, you know what I mean? I pulled some load data off the hodgdon website that I'm comfortable with and started there.

 

[.7mm.]

Try and check hole alignment with a borescope? Also look down the tube and see if it's straight or cocked to 1 side? If cocked it'll cause drag on the bcg. Another way to check that is don't let the bcg close by spring force. Tou can either open the receiver and do a bolt function test by hand (stick your pinky in the carrier and pull slightly open and then close by pushing from the ejection port. Also with the bcg back, check the tube and see if it's in the middle of the handle track/slot. Some gas blocks won't be pushed up against the journal shoulder for block and gas port alignments. This is due to either block dimensions or when gas port is reamed after being headspaced. I use (sometimes) AP blocks (adjustable and non), but don't know the port size in the blocks?

I'll check with a borescope when I get home.
I'm hoping its not misaligned. I dont really want to pull the hand guard off again.

 

[.7mm.]

What buffer do you have installed? I went with an H2 weight buffer , and could've went with an H3

BINGO
haha I've got the wrong buffer in there. Pretty sure I put a 3oz carbine buffer in that stock about a year ago and forgot about it.

 

[ARlife4me]

BINGO
haha I've got the wrong buffer in there. Pretty sure I put a 3oz carbine buffer in that stock about a year ago and forgot about it.

So, the buffer was to heavy other than to light? 3oz should act like overgassed and run the bcg to fast.

 

[.7mm.]

So, the buffer was to heavy other than to light? 3oz should act like overgassed and run the bcg to fast.

Hmm...good point. Gas port isn't blocked. But if the buffer is too light then I'm back to square one. Is it possible to be so overgassed that the bolt will slide right over the bolt catch and go back into battery?

 

[ARlife4me]

Hmm...good point. Gas port isn't blocked. But if the buffer is too light then I'm back to square one. Is it possible to be so overgassed that the bolt will slide right over the bolt catch and go back into battery?View attachment 526172

Correct