I just went through a long and difficult process of troubleshooting an AR problem. Good news is that we have solved the real problem, but along the way we had to re-learn some fundamental lessons in order to eliminate the obvious.
Now to the point: Periodic cleaning and maintenance of the AR-15 Rifle.
We all know that our AR-15 rifles need to be properly cleaned after each trip to the range. Like most, I sometimes just punch out the bore, and wipe off the bolt and bolt carrier and call it good. In my case, this has never failed me. I tend to keep a running count of the number of rounds that I put down range, and I clean the gas system every 500 rounds or so.
This was true, up until a couple of months ago. This is when my buddy and I began to reload ammo, cast about for the perfect powder / projectile / primer combo, and we would try two or three different types of ammo at a time. To top it off, we would throw in a hundred rounds or more of old Wolf .223 (which is dimensionally more akin to 5.56 NATO).
The result: A very dirty gas system, and an un-characteristic set of issues that we had not previously experienced. I want to be clear!!! These issues were self inflicted by our lackadaisical cleaning an maintenance, and the combination of two or three different types of powder which individually are fine. but in combination can cause complete failures in the weapon.
Background complete: Now for lessons learned.
Each and every time you fire your AR-15, you should take a 16" long pipe cleaner, soak it with Hoppe's, and insert it all the way into the gas tube. Place the upper in a muzzle down orientation and leave it for at least an hour, then with a pair of needle nosed pliers, agitate the pipe cleaner in and out of the gas tube. You only need to move the pipe cleaner about an inch or so, but it needs to be a scrubbing motion. Re-insert the pipe cleaner and leave the upper in a muzzle down orientation for another hour or two, repeat the above process of scrubbing. At this point, you can remove the pipe cleaner, turn it around and re-insert it into the gas tube. You will be using the dry end of the pipe-cleaner now, and you should insert it all the way into the gas tube and repeat the scrubbing motion explained above. Remove the pipe cleaner, set aside the upper, and get the bolt carrier, disassembled. Insert the wet end of the pipe cleaner into the gas key, and agitate. Make certain that the pipe cleaner is moving all the way into the bolt carrier body by looking into the frot of the bolt carrier. Remove the pipe cleaner, and fold it over so that you have a one inch long, double or even triple layer of pipe cleaner. Insert that into the gas key, and twist aggressively to ensure that you have scrubbed out the gas key.
Now, use the same pipe cleaner double or triple folded to swab the outside of the gas tube where it extends into the upper receiver. Follow up with a toothbrush or cleaning brush to remove any additional residue.
By following this process, you will ensure that you will never suffer a gas system failure. In the field, simply delete the soaking step, and swab the gas tube twice, followed by a dry pipe cleaner....Voila! A trouble free and reliable gas system.
Sometimes, we all need to be reminded of the basics. If you are anything like me, you will become complacent over time. This process is simple insurance.
By the way, 16" pipe cleaners are available at a reasonable price. Just Google "16 Pipe Cleaner".
Hope this helps...