Just a trick I learned while I was in the guard, to see if your gas rings are on the worn side. If your carrier can stand up on it's own upwright. Then the gas rings are a GO they should hold the carrier up, if they don't then it's a NO GO........
Just thought you would like to know....They call that a ..."Heads-up"

I'd say that it wouldn't be a true indiction if the bolt cam pin is still in, as in your pic.
Mine wouldn't be able to hold the weight of the carrier even if the rings were only 250 rounds old, without the cam pin in.  Yet, it's a GO.

I agree. I have a set of gas rings that are only about 100 rd old and they wouldn't hold up to this test. OTOH if you grabbed the bolt carrier and turned it upside down, the bolt will not drop out (passes that test).

My understanding is that placed in the opposite position - carrier down - the bolt should stay extended (unlocked position) and not collapse (locked position) of it's own weight.  If I've had this wrong I've been shooting thousands of rounds with bad rings!!

Sam

OK ! I getting alittle flack from people! I never said this was "Fool proof" ! This was a spot ck only..........Sooooooooooo I'll get the ARMY TM 9-1005-249-23&P manual out.
And on Page 2-30 under   Inspection/Repair

2. With retaining pin and campin removed from bolt carrier check for worn bolt rings as follows:  Insert bolt assembly all the way in boltcarrier. Turn boltcarrier downward as illustrated. If bolt assembly fall out, rings are worn. Evacuate to direct support maintenance.

OK ! I stand corrected

Mine passes the test as pictured (without cam or firing pin) after 1500 rnds or more.