Double Feed - AR15.COM

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Posted: 6/10/2005 5:59:44 PM EDT

Can someone tell me possible causes for a double feed? Didn't see anything in the -23&P. It only happens in full auto and seems to be isolated to one mag, but that mag has seen LOTS of semi-auto use is a variety of guns with no issues.

The empty case extracts and ejects, then the bolt picks up two live rounds and tries to jam them into the chamber at the same time. It happens maybe once every 2nd or 3rd mag.

The mag in question is USGI w/ green follower. I've probably replaced the spring too, though I can't be sure. Welds are solid and feed lips are straight. I've never had a round pop out the top when it wasn't supposed to.

Ammo is XM193.

Sendra lower w/ Bushmaster M4 upper.

I'm leaning toward a mag issue, but wanted to know if this might be an indication of a problem with the gun itself.

Thanks,
SC

Posted: 6/10/2005 6:03:51 PM EDT

[#1]

I have found on rare occasions, it can be a buffer/buffer spring issue too. 99% of the time, it is the mag.

Posted: 6/11/2005 12:22:50 AM EDT

[#2]

Ditto on the mag,

Just be sure it's worth rebuilding, hence check the back bolt catch slot on the mag for crack at the bottom of the U channel. If you find cracks, trash the mag and just buy a new one (got to love that you can now buy New USGI 30 round mags for less than $14 apiece).

Posted: 6/11/2005 6:18:06 AM EDT

[#3]

If everyone concurs its the mag and not something with the gun, I'll probably just relegate the mag to non-FA use only. If it starts giving me trouble in semi, then I'll relegate it to the failure-drill-training/trash heap.

Thanks,
SC

Posted: 6/11/2005 11:13:08 PM EDT

[#4]

if you have ready access to a stiffer buffer spring you could drop that in and go shoot with the suspect mag. if it's a overfunction causing the double feeds (rare as HM stated) then the stiffer spring should attenuate that.

Posted: 6/12/2005 5:08:52 AM EDT

[#5]

I'll give that a try next time I'm out. The whole buttstock setup, including spring, is suspect and will be replaced as soon as funds allow. In the meantime I can swap the spring and buffer from my semi lower for T&E. It may be awhile before I get back to the range, but I'll report back with results when I do.

Thanks,
SC

Posted: 6/12/2005 7:39:13 AM EDT

[#6]

If you are running a full auto, a heavier buffer like the MGI RRB would have other positive benefits like much improved controalibility and a reduced cyclic rate..

Posted: 6/12/2005 9:07:12 AM EDT

[#7]

HM,
I gave your over function a thought,
The only time I have seen such is when using a cheap buffer spring that loses tension when it becomes hot (when not hot, it still gauges ok). This leads to the lack of the rearward dead blow effect due to the increased rearward speed, with the buffer actual being rebounded/bounced off the back of the receiver extension (but buffer still works on lock up to prevent carrier bounce). In this condition, the top rounds are danced out of the mag (fountain effect) by the rearward impact off the buffer off the back of the receiver extension.

Is this what you were pointing out?

Posted: 6/12/2005 2:36:15 PM EDT

[#8]

Anything that can slow the function of the weapon without affecting reliability negatively will only have positive effects regarding parts longetivity and making the weapon less sensitive to marginal mags. Will give mags with weaker springs a bit longer to get the round in position if it will dwell a bit longer at the bottom of the buffer tube before it moves into the feed cycle.

Posted: 6/12/2005 5:10:04 PM EDT

[#9]

We might be on to something. The rifle is running with an H buffer, but the spring is definitely weaker than on my other semi carbines. I'll swap springs and try again with the same mag next time I'm at the range (which may be a couple of weeks unfortunately).

Posted: 6/12/2005 8:59:12 PM EDT

[#10]

Quoted:
The only time I have seen such is when using a cheap buffer spring that loses tension when it becomes hot (when not hot, it still gauges ok).

I've seen it on a kit gun that turned out to have a gas port larger than 1/8" (16" tube) with a rifle spring cut in a half and half of a rifle buffer installed. Lot's of double feeds on that one. Replacing the buffer and spring led to even more malfs due to the over large gas port. Spent several days working on that one.

Posted: 6/13/2005 6:19:59 AM EDT

[#11]

Quoted:
I've seen it on a kit gun that turned out to have a gas port larger than 1/8" (16" tube) with a rifle spring cut in a half and half of a rifle buffer installed. Lot's of double feeds on that one. Replacing the buffer and spring led to even more malfs due to the over large gas port. Spent several days working on that one.

Are you saying you don't think the slightly weak buffer spring in an otherwise reliable system is enough to cause the problem?

Posted: 6/13/2005 11:17:01 AM EDT

[#12]

where did I say that? anything is possible.

Posted: 6/13/2005 2:36:28 PM EDT

[#13]

SmallChange,

Just face up to it,

You , like the rest of use, have mags that are older than dirt (due to the old mag ban). The mag spring, and possalbe the lips of the mag have given up the ghost. Since your problems seem to be releated to a single mag, don't try to re-invent the wheel, and tweak the rifle for problems caused by the worn mag. Just spent the $14 and buy a brand new USGI mag to replace the old worn out one.

As for the old mag it's self, either rebuild it if it's worth saving, or save this mag for when you need to pratice clearing jambs (at least it's good for that just like it is).

Posted: 6/13/2005 7:04:29 PM EDT

[#14]

Just face up to it,

Never! AR Mags are like .45 brass -- unless there's a visible crack there's still life in them...

Okay, you win. Mag #9 has a date with a piece of yellow electrical tape (which denotes less-than-100%-functional mags in SmallChangeVille).

But I still plan on replacing the the entire buttstock assembly on the gun in the next month or two. Of course I'll have to see if the problem goes away when I do.

Posted: 6/14/2005 3:22:22 PM EDT

[#15]

Double check the forward top spot weld by squeezing top of mag together, any movement guaranties double feed problems.

Posted: 6/15/2005 11:42:22 AM EDT

[#16]

Quoted:
Double check the forward top spot weld by squeezing top of mag together, any movement guaranties double feed problems.

The mag would be savable if this was posted a few years back.
Ask anyone around here then and they will direct you to JB weld, then proceed to do a two page write on the clamping and bonding method.

(The real humor in this is during the ban; you would have had to try it out for yourself to see if you could have saved the mag. Thank god for replacement bodies, then the end of the ban. Too bad that you can't still get USGI surplus mags in the 20 lot bags for $10 like back in the 80's)

Posted: 6/16/2005 11:34:32 AM EDT

[#17]

Welds are good.

Too bad that you can't still get USGI surplus mags in the 20 lot bags for $10 like back in the 80's

20 mags for $10? That would have been nice.

But I would have saved my money and put it all toward M16s

Posted: 6/16/2005 3:25:17 PM EDT

[#18]

Quoted:
But I would have saved my money and put it all toward M16s

Don't even go there!!!!!
I can remember when the price on a NIB M-16 was $325, and Microsoft stock was just being offered to the public.

Funny part is I remember my dad bitching later on in life about being offered IBM stock (dirt cheap) when he first got into the service, and how he drank/whored the money away instead of buying it.
Looking back over my youth, the apple didn't fall far from the tree.

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