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Severe M4 Problems


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Hi, I recently bought a Benelli M4. After successfully putting 400 rounds through the shotgun, I have began to develop problems. After firing 1-2 rounds, the magazine cap becomes loose and the barrel will literally jump loose out of the shotgun. Obviously, I have tightened down this camp as tight as humanly possible. Does anyone have any advice on fixing this issue? Is using loctite an option or do I have other issues that are causing this problem? Thanks, Phil

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When you tighten the magazine cap, do you feel a ratcheting action as you nearly tighten it completely? Remove the magazine cap, and inspect the the end, verify that there is a small detent protruding from the end of the barrel. If you look at the bottom of the magazine cap, you'll notice teeth like serrations that the detent will engage with.

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Is the magazine cap retaining pin & spring present? This pin is what engages the detents on the magazine cap when you get it almost all the way screwed down and it starts 'clicking'. If you hear the 'clicking' it would indicate that the pin and spring are present. If they are not...there's the problem.

Edited by paladinjme
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Thanks for the replies. The retaining spring and cap are both present and appear to be functioning as designed. The retaining pin has spring pressure and the teeth on the cap engage the the detent spring, but the cap still comes loose when firing only. The threads all seem to be intact with minimal wear and no stripping.

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I think tktm might be on to something.

If the handguards didn't allow the barrel extention to seat properly into the receiver

it is conceivable the mag cap wouldn't have enough threads exposed to seat on??

Just a wild guess.

 

Can you post pics of the receiver/barrel interface and the cap?

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Replace your aftermarket handguards with the OEM handguards and repeat testing. Let us know if the problem persists. I do not think it will.

 

Other than that, I have read this thread and am at a loss. I assume that the problem is not you, and I cannot figure out how it is the weapon, if the detent is present, and nothing looks grossly "wrong", and you are getting audible and physical feed-back when you tighten the cap.

 

Take a picture of the barrel/receiver joint after it is installed, and take a picture of the detent and cap where we can see the detent, see the teeth. Take a picture up into the receiver's "ceiling" with the trigger-group removed. Take a picture of the handguards with the shotgun upside down (fully assembled), and looking down on them right-side up. This will allow everyone to see every possible failure point except for something really outlandish.

 

Those are the only areas that I can think are the issue. The only other issue is that you are using the OEM 2-piece setup for the mag-tube with the spacer, and your spacer is loose, so no-matter how tight you get the mag-tube, the spacer being loose negates it. I studied that as a failure point, and it is one. Insure that the spacer is tight to the magazine tube, if that is your setup, before you tighten the cap.

Edited by Unobtanium
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I think tktm might be on to something.

If the handguards didn't allow the barrel extention to seat properly into the receiver

it is conceivable the mag cap wouldn't have enough threads exposed to seat on??

Just a wild guess.

 

Can you post pics of the receiver/barrel interface and the cap?

 

If the handguards he is using are slightly "longer" and prevent complete seating of the barrel in the receiver, then they are taking the brunt of the recoil instead of the receiver. They are polymer I bet, and they flex. This takes tension off of the detent/mag-cap. This allows movement of the mag-cap.

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Check put this problem forum member Mean Green had with hand guard fitment. On page 5 of my KZ review he discovers cause of the issue (barrel not fully seating see page 4 of thread)that was described earlier in the thread I believe this could have lead to loosening if the weapon had been fired in this condition

 

http://www.benelliusa.com/forum/showthread.php/19590-KZ-U-S-made-forearm-review/page5?highlight=Kz+review

Edited by Hookster
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If you are using non factory hand guards (forends) they are likely too long. I have seen this before from a couple different aftermarket company's products. what happens if they are too long, is like the other fella said, the barrel extension does not fully seat in the reciever. then when you shoot it under recoil the barrel moves slightly (fractions of an inch) and this will cause the cap to loosen. I would put the factory parts back on and shoot the gun. if there is not problem, its clearly the aftermarket parts. If it still does it with the factory parts, call benelli's customer service they are great.

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I am not using the factory handguards. How would an improper seating of the barrel in the receiver force the magazine cap to loosen? Once again, thanks for all of the help and the replies

 

I warned about this concern with FFT handguards back in Feb of 2011. see

http://www.benelliusa.com/forum/showthread.php/25750-FFT-forend-review?p=150641#post150641

It could happen with any manufacturer's poorly fit handguard. Unfortunately, you are about to see the bad side of this board come out as shills will popup and attack shortly in an effort to protect marketshare.

 

The issue comes down to the fact that the magazine cap's function does not include force fitting the barrel into the receiver. If the hand guard dimensions are off enough to prevent the full and proper seating of the barrel into the receiver, the handguards end up becoming a structural part of the gun.

 

Obviously Benelli did not design the handguards to be a structural part of the receiver / barrel fit. Nor did they design the magazine cap to be used as a torque nut to force poor quality out of dimension handguards to fit. With that in mind, the action of shooting the gun puts more load on the handguards than you can possibly hope to do by tightening down the mag cap; as a result the handguards distort enough that the mag cap can loosen.

 

Just be glad that nothing worse happened.

Here is a video of the issue I had with the FFT handguards

Edited by TKTM
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