My new AR build is short stroking.

[uncle money bags]

It may be an oddity, but its a wrong oddity. There is no reason that should be shorting with the description of the system you gave. I assume there isnt any unusual dragging or binding when you charge it?

If not then its a gas issue. Did the upper come with the 13" vtac from BCM? How did you check the port size under the gas block? Is it possible the gas block was mounted wrong after the port size was checked?

I ask because on the bcm middy I had; when the gas port on the barrel and gas block were lined up, the gas block itself was behind the ledge of the barrel stop about 1.5 mm. It didnt look right to me but when the gas block was all the way forward to the stop it cut off some of the barrels port.

 

[Hump66]

I added the VTAC. No drag/binding, smooth as butter. Port size checked with digital calipers. I'll have to check the gas block placement again I guess. I mounted it just like I have all my others, which have no issues.

Pic looks like it was lined up right:

 

[uncle money bags]

Yep, sure does.

that eliminates the usual culprit. Gotta work your way back from there looking for leaks. Im 99% sure that you will find a gas leak. any unusual carbon deposits around the gas block or tube?

how about a pic of the gas tube on the other end where it mates with the BCG gas key.

 

[Hump66]

No apparent carbon around the gas block. Here's the other end:

[Broken External Image]

 

[uncle money bags]

Are you using the gas block that came with the barrel?
Is there any obstruction in the passage?

 

[Hump66]

I had to add it to run the VTAC, it's a low profile. Clean and clear. All my AR's are set up exactly the same, but this one is the only one with issues.

 

[uncle money bags]

I know this is going to sound strange, but since you have the gun apart can you install the gas block and pin the tube in place. Then blow through the tube from the BCG side and check the flow?

Seriously, there is a method to my madness!

 

[Hump66]

Sure. I'll report back in a minute.

 

[uncle money bags]

cool. another thing I should have asked before. Did you shoot this gun before the mods were made?

 

[Hump66]

Ok, no excessive pressure required, air flow is good.

cool. another thing I should have asked before. Did you shoot this gun before the mods were made?

Actually no, bought the complete upper and swapped the parts as soon as it showed up.