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Loose magazine cap while firing


Sigfla

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1 hour ago, Sigfla said:

Anyone have a fix? I just took a class today and my M4 cap kept loosening up despite my tightening it down hard. Am I missing a trick? 

 

Personally, i think that they just do. No matter how hard you crank the cap down, after a hundred+ rounds, it's not gonna be as tight as you had it before firing. I posed that question here a looooong time ago and people were like; "huh", whaddaya mean? I never notice that". Then over time more people have posted about it.

So maybe it's just the gun or maybe I don't know but, I know that it happens.

I think it's possible that the ball detents on the cap could be cut just a wee bit deeper? They are pretty shallow cuts.

Some advice given has been to push the barrel tight up against the receiver before beginning to tighten the cap as opposed to just letting the cap as it screws down take up that last 1/8" or so before the barrel is flush against the receiver. 

Edited by Evolution
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I am concerned that I somehow didn’t install the new 7rd magazine tube correctly. I can’t see how having it screwed in too much or not enough would cause the loose cap though. It seems like it’s on tight enough so I can’t imagine it’s unscrewing itself from the cap??? It’s such a simple thing I can’t figure how it doesn’t stay tight with the detents 

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3 hours ago, Evolution said:

Some advice given has been to push the barrel tight up against the receiver before beginning to tighten the cap as opposed to just letting the cap as it screws down take up that last 1/8" or so before the barrel is flush against the receiver. 

That's a good idea. Another thought would be to put an O-ring on before the cap. By compressing the O-ring it would create tension which might help keep the cap tight? Buna O-rings are only good up to 180-200 F you might want to try Viton which is good to 400. It's just a thought?

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I have never had one of these mag caps come loose? I use my retard strength on the cap to make sure it is seated fully and that the barrel is firmly seated against the face of the receiver. My concern would be that the barrel isn't seated fully in place and it is allowing the barrel assembly to move during recoil.

I'd check the detent that is in the end of the barrel that ratchets on the teeth of the magazine cap. You should be feeling resistance to unscrewing the cap.

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1 hour ago, StrangerDanger said:

I have never had one of these mag caps come loose? I use my retard strength on the cap to make sure it is seated fully and that the barrel is firmly seated against the face of the receiver. My concern would be that the barrel isn't seated fully in place and it is allowing the barrel assembly to move during recoil.

I'd check the detent that is in the end of the barrel that ratchets on the teeth of the magazine cap. You should be feeling resistance to unscrewing the cap.

So after reading this I decided to grab the gun out of my case and give it a good look. I noticed my IWC light mount was loose (not surprisingly bc I didn't loctite it down). I have a bad habit of dry fitting things and moving on without locking them down properly. I took the gun apart and fixed the loose IWC screws with lock tight. I then took a look at my FFT magazine tube. Low and behold it was loose. I could unscrew it by hand without any force. I broke out the blue lock tight again and really torqued it down with a little drop or 2 of lock tight. I doubt its moving now. I did notice the cap teeth are cut super shallow though. They are almost decorative really as they only engage on the outside edge of the cap. Anyway I think its fixed. 

Had a good day in class with the gun but we weren't using slings and I am not doing that again with the Benelli. I found myself reaching for my Beretta 1301 more often just bc of the weight standing on the line.  

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If you look at the face of the barrel hanger that the cap seats against, you should find a small detent that protrudes from the barrel. This is meant to give the teeth on the cap something to catch on. If I recall, the detent has a spring behind it and the spring and detent are staked in place.

The Loctite should do the trick to hold the magazine tube in place. Figure if the tube is loose at all, it can let the mag cap move as well.

I have a routine where I coat all screws and threaded holes with Loctite primer. Let the parts dry, then apply the appropriate strength thread locker to the parts. Tighten to a spec if one is known. Sometimes I'll use a silver Sharpie to mark the screw and the mounted object to give me a witness mark to see if the screw is moving.

A rifle/shotgun without a sling is like a pistol without a holster.

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