Ok, so I have put together this rather ordinary 20" rifle AR-15. Nothing special, nothing weird. It short cycles BAD. Bolt slips over the magazine without picking up the next round, and just goes "click", weak ejection, just weak, weak, weak. I have only tried two different ammos so far (PMC bronze, and now some Armscor USA), and they both perform exactly the same. I assumed it was "undergassed". So....
At first, I noticed some gas blast on the front end of the gas tube, and figured it was leaking out there (after looking at other rifles that function perfectly, they also have the same bit of gas blowby marking). Well, the hole in the front sight block is within spec (supposed to be right at .180", which it is). I changed the gas tube. No effect. Still short cycling. Ok, well, maybe the buffer or spring ain't right, so I changed them with another Rifle buffer and spring I had. No effect. Still short cycling. Ok, maybe something is wrong with the bolt.. excuse me... "bolt carrier group". It's a brand new Expo Arms Microbest bolt. Quickest way to check that is to simply change the bolt... excuse me ... "bolt carrier group". So I put in one from a PSA rifle that works perfectly fine. No effect. Still short cycling. Well, schidt. What's left? The gas port in the barrel.
The spec gas port size for a normal 20" rifle with a .750" gas block journal is .093" to a max of .096". So, I take the front sight off and using drill bits as gauges, I took one that actually measured .093" and found that I could probably force the bit all the way into the hole, but I wasn't going to do that. So the hole is the proper spec size (as the manufacturer said it would be drilled at .093"). Well... ok.
I put the gun back together. At first, I was shooting with PMC ammo, which is not super high powered anyway, though I have NEVER had any problem with it before. I wondered if maybe it was a bad batch of ammo, so changed to different ammo. No effect. Same thing. The gun should not be that damn picky about ammo anyway.
Am I missing something? Basically EVERYTHING has been changed except the barrel, and the barrel seems perfectly fine, and it still does the same thing.
