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Benelli M4 Malfunctioning


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After a few modifications to my new M4, I tested it today and found that it is not working properly. I thought at first that I had bad ammunition. It sounds as if the hammer is striking the firing pin, but there is no evidence on the primer. My modifications to the M4 are as follows:


New single piece seven shot magazine tube

Mesa Tactical 8 shotshell carrier

FAB picatinny rail forend


After the initial modifications of the shotshell carrier and forend, the M4 operated flawlessly. The only thing that I have done after that is replace the magazine tube.


Now, about every 2nd or 3rd shot it malfunctions. As I stated before, it sounds as if the hammer is striking the firing pin, but no evidence of the pin striking the primer.


Anybody out there with insight to what might be going on?

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Guest cleefurd

None of the mods, regardless of manufacture could cause the afore-mentioned malfunction due to their CORRECT proximity alone... unless....


... there exists one that prevents an un-blemished firing pin from reaching the primer via a harmonious bolt, and you have your culprit...

Check to see if any divulged mod's;


  • Distort the receiver
  • Prevent the barrel from fully seating adjacent to the receiver, (or lastly)
  • Inhibit the bolt/carrier from attaining full battery

Beyond that, do a side-by-side/ selective inter-change with a verified firing pin BC group.

If none of the above bear fruit, check for an "aft seizing" piston.


Then....the dreaded geometric frocksidazical trigger group-matrix wields assymetric dillemas galore.... oh the horror.

Edited by cleefurd
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I'd disassemble, clean, LUBE and reassemble. Really hard to see a causal link to your mods and this. Maybe something not fully seated or sticking when you put it all back together.


I know, very little help but this is a strange one. If you said, rounds were't feeding that might be a different story. You sure it sounds like the hammer is falling?

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Your problem is the FAB Defense rail/handgaurd. First of all it is crap, secondly it was designed for the Gen 1 M1014, not Gen II 11707 or 11717's. You can make that forend work with some time and a dremel tool, but since it is a really ****** part it's not worth the time.


Change back the OEM handgaurds and retry.

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  • 3 weeks later...

Several issues sound like the same I had. I know this sounds redundant, but clean the gun and especially the inside of the tube very well, mine was nasty and caused feeding issues. If you used Dave's springs, they do not work, get a factory spring or Kip's spring to really safe. I have one of Kip's tubes on order now. As for the Fab forearm, I agree, ditch it. It causes issues with your gas piston action. Surefire is good to go.

After changing my spring out, cleaning the crap out of tube and putting the surefire forend on, it is flawless. If your not going into battery, it could be short stroking the bolt due to the gas pistons being hindered.

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