Hi guys, I just bought a 16" .750 barrel that has had the gas port worked on . It is currently .063 and reportedly works and functions OK with the exception of not  locking back after the last shot. I was going to have the seller open up the gas port to .067 prior to sending me the barrel. I have been informed the minimum post size for a 16" .750 barrel is .070 and the minimum size of a .625 16'" barrel is .063. It appears this may be s a 16" .750 barrel with a gas port for a .635 barrel. What info do you learned guys have that may help me about the size of a standard gas port or a 16" barels (is thier a defference for different barrel diameters? and what size is the gas port hole in the barrel supposed to  be for this barrel?....Thanks....<><....:)

How was the gas port "worked on" when it is at the starting spec of 1/16 (.063)? The not locking back could be magazine or ammo related.  Ensure mags are good to go first.  Ensure recoil buffer is standard weight.  Ensure gas block is aligned and tight.  Ensure rifle is cleaned and well lubed.  LASTLY, then open port by .001-.002" at a time, rechecking intended loads thru different magazines.

also make sure the bolt catch is working free in the upper before you start working on the gas port
I had one build that I almost worked on the port but luckly found the bolt catch was sticking a little bit and not locking the bolt open.

If I read your post correctly,

You have bought a barrel, but not received it yet. correct?

The functioning problem is on the sellers gun not yours. correct?


If both of the above are true statements, I personally would see how the barrel worked on my gun before messing with the gas port size.  It's much easier to make a hole bigger than it is to make it smaller.