11.5" AR Crushing Cartridges

PoFF

PoFF

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I was wondering wether to start this thread in the Black rifles section or Gunsmitthing, so if this is at the inappropriate section, please feel free to relocate it.

While firing my AR last weekend, a few jams occured, which was a first for me, as this gun never jammed on me before. I used to feed it Remington UMC 55grs FMJ cartridges via a Thermold magazine with no problem, last weekend I've switched to Winchester USA 55grs FMJ, via brand new Brownell's aluminium magazines with green follower. The failure rate was 4 rounds over a total of 50.

Now the jams themselves, it looked like that immediately after firing, the spent case extracted and ejected correctly, like it should, but on the return trip, the bolt partially stripped a new catridge from the magazine, enough to get the bullet (just the bullet, not the whole cartridge) past the feeding ramp, then the bolt slipped from the back of the cartridge, to continue it's forward motion and hit the cartridge on the side, bending it to a point it is now "unchamberable". I didn't have my camera at the time, so no pics, but I hope the description is detailed enough for diagnosis.

Would this problem be related to the new magazines, to the ammunition, or simply to the gun itself?

Any advice will be greatly appreciated.
 
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magpul followers needed

PoFF said:
I was wondering wether to start this thread in the Black rifles section or Gunsmitthing, so if this is at the inappropriate section, please feel free to relocate it.

While firing my AR last weekend, a few jams occured, which was a first for me, as this gun never jammed on me before. I used to feed it Remington UMC 55grs FMJ cartridges via a Thermold magazine with no problem, last weekend I've switched to Winchester USA 55grs FMJ, via brand new Brownell's aluminium magazines with green follower. The failure rate was 4 rounds over a total of 50.

Now the jams themselves, it looked like that immediately after firing, the spent case extracted and ejected correctly, like it should, but on the return trip, the bolt partially stripped a new catridge from the magazine, enough to get the bullet (just the bullet, not the whole cartridge) past the feeding ramp, then the bolt slipped from the back of the cartridge, to continue it's forward motion and hit the cartridge on the side, bending it to a point it is now "unchamberable". I didn't have my camera at the time, so no pics, but I hope the description is detailed enough for diagnosis.

Would this problem be related to the new magazines, to the ammunition, or simply to the gun itself?

Any advice will be greatly appreciated.
Click to expand...



Get MAGpul followers anti tilt had the same problems with my shorty as the green tilt, as the shorties are faster cycle rate. hope this helps.
 
sigger69 said:
You need a Wolff extra power extractor spring.

Winchester USA is hotter than UMC.
Click to expand...

I'm wondering in which way an extra power extractor spring will help me, the cases are extracting and ejecting just fine, it's the next cartridge feeding that's proving problematic.
 
Could it be short-stroking? The bolt is probably never clearing the magazine on the way back, and going forward it rubs the top round, moving it forward and then jamming.

If Winchester is hotter than UMC, it's unlikely, but that what it sounds like to me.
 
Sounds like your rifle is short stroking!!! The bolt does not have to go all the way to the back to eject the fired case, it does have to go all the way to the back to load a fresh round properly. One question, does it lock open on the last round??

Scott
Dycor Special Services
 
Yes, the bolt locks open flawlessly at every last shot.

How would I fix short-stroking? Weaker spring? I might give it a try to see if that's really the problem. But as Kirill, I doubt it is the problem, if Win USA is really hotter than UMC, I wouldn't see how it would shortstroke with the hotter stuff while it doesn't with the weaker.
 
PoFF said:
Yes, the bolt locks open flawlessly at every last shot.

How would I fix short-stroking? Weaker spring? I might give it a try to see if that's really the problem. But as Kirill, I doubt it is the problem, if Win USA is really hotter than UMC, I wouldn't see how it would shortstroke with the hotter stuff while it doesn't with the weaker.
Click to expand...

here's a crazy idea: maybe your magazine spring is not strong enough to push the cartridge up in time? What if you jammed some stuff on the floorplate of the magazine to compress the magazine spring a little bit?
If that solves the problem, then maybe the recoil buffer spring has to be changed to a weaker one to allow the bolt carrier to move back further and allow more time for the next round to come up.

Crazy, but might work. :redface: :redface:
 
How are your USGI mags pinned? If its through the spine there is a chance that the spring is hanging up on it on the inside (on the rivet) thus reducing the spring tension on the follower. You can pop the base plate off and "hook" another bit of the spring over the rivet to add more pressure...hard to explain but that may help.....
 
Kirill has got the essence of the problem. This is the common cause of this sort of misfeed in any semi-auto.

The round isn't rising fast enough, or conversely the bolt is cycling too fast.

To cure you need to make the round rise faster, either with a stiffer spring, or smoother/better finished/better pinned/cleaner mags.

Or you need to slow the bolt cycle time with a heavier buffer/lighter buffer spring/heavier bolt carrier.
 
Magazine spring hanging on the rivet... this is brillant. Never even remotely came close of thinking about this one...

If this fail, stuffing a spacer at the bottom of the mag it will be...

If this also fails... well, some parts replacement will have to be done...

Thanks a bunch for all that info guys.
 
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Definetly a magfeed problem...
Kirill maybe right, some mags have a tendency to have the follower 'bounce' the ammo on the lips of the follower, therefore making it loose contact with the bolt on feeding.
 
PoFF said:
Yes, the bolt locks open flawlessly at every last shot.

How would I fix short-stroking? Weaker spring? I might give it a try to see if that's really the problem. But as Kirill, I doubt it is the problem, if Win USA is really hotter than UMC, I wouldn't see how it would shortstroke with the hotter stuff while it doesn't with the weaker.
Click to expand...

M16's are famous for bolt over base malfunctions, caused by their crappy magazine design. I had the exact same problem with my AR15. Never did solve it. I tried stretching mag springs, etc etc.
I recently got to fire a full auto M16 in Vietnam- exact same problem. The mag/gun combo lends itself to that issue unfortunately.
Quote(Most of the firing sequences were conducted with Portuguese M193-type ball ammunition of 1982 manufacture (headstamped 'FNM 82-17'). What a pleasure it is to fire an assault rifle in this caliber and not have to contend with bolt-over-base stoppages such as those induced by an M16 magazine. There were no malfunctions of any kind.)
 
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