Here's one for you?? I'm baffled.

[Thumper580]

Of course its saturday so i cant call anyone...
brand new custom build TBox barrel with matching bolt, after 10week wait...it looks wonderful..
brand new SLR adjustable gas block and melonite gas tube..

install barrel and gas block...just like 100 times before.... gas block fully open... gun won't cycle!!!!!
check alignment on everything and all is straight..
remove gas block and tube... easily blow air through the tube and out the block.. ok..
check the gas hole on the barrel and, yes it does go all the way through.....
I measured the gas port distance from the shoulder on my old barrel (.300"). measured the new barrel and got the same..
SO... gas flows out of the barrel port and air flows through the gas block and tube, but it wont cycle the gun????

Any ideas??? I've had a boatload of AR's and never this...

 

[Bigjake83]

Need to know more.... What is it exactly doing, is the bolt moving to the rear at all??? is it short stroking not picking up the next round?? is not unlocking all?

Are you using the correct length gas tube??
Is the gas port on your new barrel the same size as the old barrel??

Does it function manually, can you load a round manually and extract it with the charging handle with no problem??

 

[Thumper580]

bolt is not moving at all, its a single shot right now.
it is a rifle length gas tube
you can easily extract a fired or unfired round with the charging handle.
the gas ports "look" the same I will measure.

The BCG moves back and forth in the upper smooth as silk (no mag, unloaded)

 

[Thumper580]

The gas port was smaller on the new barrel vs the old one. I opened it up to the same size as the old one and will test tomorrow.

 

[Bigjake83]

The only other variable is the Gas Key on the BCG, make sure there is nothing obstructing gas flow in your BCG. I had a JP BCG come to me one time and the gas key was completely filled with cardboard.

 

[Thumper580]

It was the gas port....to small (.052"). I opened it up to .092 and it works fine.

 

[2ndamendfan]

.052 is pretty small. Just want to say thanks for posting the fix. So damn frustrating when the fix is never posted. Leaves everyone hanging and everyone knows someone isn't going to live with a problem like that.

 

[Thumper580]

turns out a 20" heavy barrel should have a gas port between .090"-.095".......

 

[ajwcotton]

Port size on an spr is .100