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Page AR-15 » Troubleshooting
AR Sponsor: bravocompany
Posted: 10/2/2017 1:51:46 PM EDT
Was a D&H magazine

Brand new M&P sport II, only tried 3 mags total:

1 Magpul: works
2 D&H: 1 works perfect, other jams first shot


What little I know:

-It feeds fine from pulling charging handle
-it inserts fine with no noticeable toughness
-it seems to be somehow blocking the bolt from cycling rearward

It's not ejecting, the bolt is about 1/2" out of battery.

Any ideas? I'm thinking the mag is dragging on the bottom of the bolt?
Link Posted: 10/2/2017 10:41:42 PM EDT
[#1]
Link Posted: 10/3/2017 1:13:13 PM EDT
[#2]
Probably nothing wrong, except the gun needs some break-in cycling to reduce internal friction and allow it to function correctly.

The magazine that does not want to work, probably just has a stronger spring than the other two, and the buffer spring and gas system do not have the strength to overcome the extra friction.

The gun is designed so the ammo rounds in the magazine (or the magazine follower) make contact and pushed by the bolt lugs, will drag on the bottom of the bolt carrier (or the magazine follower).  This is how the gun loads the next round to fire, and stops with the bolt held open on a empty magazine.

The tension of the buffer spring, and the port size of the hole in the barrel control how much gas and spring tension are available to cycle the action.  It's a delicate balancing act, and the additional friction present in a new gun that has not polished it's working surfaces is going to have more internal friction than a properly broken in gun, and that can make all the different in the gun's function.

During the 300-500 round break-in period, using good quality, full power ammo is recommended for functioning.  That would be U.S. made, preferably Federal or Lake City 5.56mm M855 or M193.  Much foreign made budget ammo is underpowered, as is Remington .223 ammo and not recommended.

You can kickstart the break-in process by "dry-cycling" gun.  Shotgun the receivers open, use a rag to wipe the bolt carrier group, and the Upper Receiver dry of lubricant, then using the charging handle to cycle the gun's action about 500 times.  Then use a rag to wipe the insides of the Upper Receiver clean, and lubricate as normal.  If you cycle the gun then, you will feel the gun is smoother.
Link Posted: 10/9/2017 12:40:44 PM EDT
[#3]
Discussion ForumsJump to Quoted PostQuote History
Quoted:
Pull the mags apart, and CLP clean them.

As for the questionable mag, see if just cleaning it solves the problem (which it may since it may be fouled with shop debris when it was assembled new).

Also, when you have the followers out, not a bad idea to clean up molding skirt flaws with a razor knife do they do not bind on the inside of the mag, and run your finger down the bottom of the feed lips and the front inner edge of the mag.  If burs are found, remove them as well.  Lastly, when you are done cleaning the mags, towel dry them.  Even when towel dried, there is enough CLP left behind to keep the springs from rusting.   As  for cleaning your mags, all depends on the round count through them, but 500 round through a mag is a good time to pull them apart to re-clean them (or if the mags are going to sit for while before being reused the next outing some weeks later)

To add, when you load the mags, make sure to rasp the back of the mag body off your hand/bench to pack all the rounds in the body to the back of the mag.  When the rifle is self loading out the mag, the recoil and the bottom of the carrier will keep the mags back, but when you are loading, can have a funky stack/top round to the front of the mag.
View Quote
I'll try that, deburring the follower and cleaning it out (I already tap the spine of the mag when loading)

I don't know how common a bad mag is ?

The first mag I ever used was the Magpul but I wanted something metal.

The first D&H was a delightful dream of a mag lol but I've never seen anything like the second.

I could understand a feed problem or even a weak ejection due to mag but the thing damn near becomes a bolt-action lol (not even an ejection!)
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