Gas ring test is to put the bolt pull out upwards with the back of the carrier on the table ,and see if the bolt weight itself will drop the bolt on the carrier from not enough gas ring tension.
Not the weight of the carrier pushing down on the bolt instead.


By the numbers since I doubt that you need to rebuild anything on the rifle (only 4K of rounds), but instead just do a good cleaning and check for gas leaks.

Pull back on the charging handle, and look where the face of the bolt stops against the back edge of the ejection port window.  The correct distance should be face of the bolt 1/4" to 1/8: in front of the ejection port window back edge.  If needed, pull the buffer and spring, and start dropping quarters down the tube as shims to get the bolt face to stop the correct distant on a full charging handle pull.  If you want the permanent solution, it to pull the receiver extension to shorter the end of it to allow it to be threaded into the receiver more instead.

On the upper, use a chamber brush with CLP and clean the chamber by hand.  While you have the CLP out, put a few drops between the end of the gas tube to gas block, gas block front and back to the barrel, and charge the gas tube from within the receiver with a piece of rubber tubing to about 100lbs of air, and looks for leaks of the gas block against the barrel, and the gas tube in the gas block.  On the B/C, few drops on the sides of the key, hold the bolt in, pressurize the front of the key with 100lbs, and make sure that the key is not leaking at the top of the carrier (read snapped key bolt).

Now pull the B/C apart, pull the extractor, and make sure that the grabbing claw of it is still sharp and the extractor spring still has plenty of tension.  After you have cleaned the B/C and have it back together, hook a spent case on the extractor, and cam the ejector in a few times flush to the bolt face.  The ejector should be under a lot of spring tension, but should not be binding up as it moving in and out of the bolt face channel.  If the extractor is binding, then you may luck out by adding CLP to it back weep channel on the side of the bolt and working it in and out via the spent case, or you may have to pull the extractor to clean the channel instead.


As for once the entire rig has been correctly cleaned and the upper receiver bearing areas CLP lubed, load only a single round into a mag and shoot the single round with the empty mag still in the well.  The bolt should lock back on the bolt catch (bolt catch in front of the bolt, and not just under the carrier holding it back), with the spent case traveling about 10' to 15' out.  Now go find the spent case, and take a good look at the spent case rim for any kind of bending of the case rim from the extractor.

Hence not enough gas and the rig will short stroke with the case rim not bent.  Too much gas to open the bolt too fast, and the extractor will bend the hell out of the rim on the spent case pull instead.
Note, chamber not scrubbed correctly during cleaning (fouling removed all the way to the last of chamber cut) will end up with a bent spent case rim as well.  If you want to know if you are getting the chamber correctly cleaned via scrubbing by hand (all the way to the last chamber of the chamber cut), then  new/clean 30 cal mop with a hint of CLP on it spun deep into the chamber.  If pull the mop out and find it fouling, your not scrubbing the chamber correctly to remove the fouling at the last of chamber cut.

As for mag release, make sure that the end of the threaded section is flush with mag release button.

One last item, and clean and check you mags.   The mags should be pulled all the way down to CLP clean them about every third firing use, as well as checking the mag lips and back U channel as well.   Really, the easy test to see if the mag is not the problem, clean and fully load the mag, then give the bottom of it a good rasp off something like a piece of wood.  If the mag fountains the rounds out of it during the rasp, you got problems with the mag with either problems with the feed lips or the follower spring tension becoming too weak isntead.