Need help with a FTF issue

[Bigd7467]

I have a S&W Magpul AR with the mid length gas system that has recently developed a failure to feed / double feed issue. I have approx. 750 rounds through the rifle with no memorable malfunctions. While attending a training course the rifle functioned flawlessly on PMC ammo the first day. The second day with the same ammo the rifle began failing to feed, it would extract the spent case most of the time (had only a few double feeds) and either pick up the next round at the back 1/3 causing a partial feed or not feed a round at all. The rifle is also failing to lock back on an empty mag. This leads me to believe that it is short cycling. I tried a different Bolt and Carrier group with very similar results. Only changes between the two days was the addition of Ranger Plates to my P mags and a light coat of grease on the buffer spring ( I cleaned all grease off and the issued continued). The second day was also about 25 degrees cooler( about 45 degrees with light snow). I appreciate all the help I can get.

[ray1970]

I was going to suggest checking the gas rings but if you tried a different bolt you can kind of rule that out.

[sportbikeco]

Ive had a piece of bullet jacket choke up a gas system.

[BPTactical]

Check to make sure the buffer tube vent is clear. Did you happen to get mud/dirt in it? Depending on what buttstock you are running if it attached with a screw there should be a vent hole in it, make sure it is clear.
Swapping BCG's tells a lot and if the malfunction continued you can rule that out.
Gas block shift?
Gas tube pinned correctly?

[Hoser]

Add oil. Lots of it.

Run it wet.

[BPTactical]

Add oil. Lots of it.

Run it wet.

Agreed

[rkfulgor1]

As above , I would check for a foreign body in the gas tube, try to clear with air, I like to use the canned air, but if your set up for it a compressor would free a blockage... Also, check for new scrapes along your BCG..see its thats where its hanging up..Was your gas block bumped or jarred at all..may have bumped it off the gas port on the barrel... OIL OIL OIL

[Bigd7467]

Thanks for all the good info guys. I took the rifle to Bowers Tactical and they said my gas rings were shot. They replaced them and I ran the third day without a single malfunction. My only thought about having the same malfunctions with the other BCG and bolt was that it was a brand new unit and not broken in yet. It's crazy that a $2.50 part caused me a full day headache.


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[BPTactical]

750 rounds should not be enough to warrant rings, if it was I would have to replace them every other time I go shooting. The ones in my 6920 probably have a couple thousand one them and they still have good tension.
Keep the rings wet as well.