AR15.Com Archives
 Gas port size
balloo93  [Team Member]
5/16/2011 2:35:33 PM
So I ordered one of the Adams Arms clearance items from Spike's tactical. **This in no way reflects on Spike's by the way.**

These barrels are meant to be used with a piston conversion. This is a 16" barrel with Mid length gas system. i am running DI on this barrel as it was mentioned that it would "probably" work. Well, it don't I am running a FA carrier and a H buffer. I don't want to go lighter on either for the sake of swapability between my other rifles.

It cycles enough to eject the round it fired, but not enough to grab the next round, so short stroking. I did play with the gas block location, and it's not that. So I read that the gas port needs to be opened up and that someone else had the same issues and a port size of .067 got rid of the problem.

So I swing by a shop that can do the port job, but they freak out when I mention .063 or .070.

So what size can I run on this sucker to allow me to shoot cheap and higher end stuff?

The melonite coating on this barrel has made it slightly larger in the fact that a .750 gas block would not fit without removing some off the inside with a sanding drum. The M4 ramps are also a tiny bit thicker compared to the receiver as well. Still feeds, so I'm not messing with that.
Krylancelo  [Team Member]
5/16/2011 2:43:31 PM
Why are they freaking out when you mention port sizes of 0.63 or 0.70?
tailwind5sw  [Member]
5/16/2011 2:50:03 PM
Just went thru this on a barrel I moved the gas port on. If its electing and not feeding use a numbered drill bit to find what size you have and go up 1 or 2 sizes. You only need a little more gas to get it there. This worked for me on a 300 blackout barrel I had rechambered to 7.62x40wt and a carbine gas 5.56 that I had ADCO profile and mine the gas port to intermediate length. Made both real smooth.
balloo93  [Team Member]
5/16/2011 2:57:50 PM
Originally Posted By Krylancelo:
Why are they freaking out when you mention port sizes of 0.63 or 0.70?


Don't know? He was saying it should be .05 and I'm telling him .06 is too small. I'll head over there today or tomorrow and drop of the barrel. I honestly think the melonite is making teh port size smaller than it should be.

From the charts I've been reading, even .080 is a reasonable size.

So if the port is too big, the cycling just becomes more violent right?
jhud  [Team Member]
5/16/2011 3:02:31 PM
Originally Posted By balloo93:
Originally Posted By Krylancelo:
Why are they freaking out when you mention port sizes of 0.63 or 0.70?


Don't know? He was saying it should be .05 and I'm telling him .06 is too small. I'll head over there today or tomorrow and drop of the barrel. I honestly think the melonite is making teh port size smaller than it should be.

From the charts I've been reading, even .080 is a reasonable size.

So if the port is too big, the cycling just becomes more violent right?


If the port gets too big, compensate with a heavier buffer.

Have you tried it with a standard buffer?
jrh308  [Member]
5/16/2011 3:03:12 PM
Had the same problem on two 20 inch uppers. Went from .093 to .096 no more problems.Checked my factory ds 20inch upper and it was .096 from the factory.
balloo93  [Team Member]
5/16/2011 3:05:14 PM
Originally Posted By jhud:
Originally Posted By balloo93:
Originally Posted By Krylancelo:
Why are they freaking out when you mention port sizes of 0.63 or 0.70?


Don't know? He was saying it should be .05 and I'm telling him .06 is too small. I'll head over there today or tomorrow and drop of the barrel. I honestly think the melonite is making teh port size smaller than it should be.

From the charts I've been reading, even .080 is a reasonable size.

So if the port is too big, the cycling just becomes more violent right?


If the port gets too big, compensate with a heavier buffer.

Have you tried it with a standard buffer?


My other three ARs run heavy to 9mm buffers. I don't want a prissy upper that only runs on one combo of parts. The other uppers run with any of the other lowers installed.
badazzar15  [Industry Partner]
5/16/2011 3:15:21 PM
Originally Posted By balloo93:
Originally Posted By Krylancelo:
Why are they freaking out when you mention port sizes of 0.63 or 0.70?


Don't know? He was saying it should be .05 and I'm telling him .06 is too small. I'll head over there today or tomorrow and drop of the barrel. I honestly think the melonite is making teh port size smaller than it should be.

From the charts I've been reading, even .080 is a reasonable size.

So if the port is too big, the cycling just becomes more violent right?


There isn't an AR out there with a gas port that small, unless it was drilled to small..

The gas ports are done after the Melonite.
mar151011  [Member]
5/16/2011 5:08:36 PM
I bought the same barrel from spikes. I used a 5/64 = .078125" cobalt drill bit on my drill press. It runs like a champ with an H buffer..
balloo93  [Team Member]
5/16/2011 7:21:22 PM
Went back over there and the guy admitted the port was small. They bored it out to almost .080. Out the door it was $12.

He said he pulled the gas block off of a RRA mid length and that was the size it was from the factory. My RRA middy runs like a raped ape so i expect this will too.