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Old January 26, 2014, 08:30 AM   #1
takem23
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moss 930 doesn't cock firing pin

My mossberg 930 fails to fire occasionally. Maybe once per box of shells. Cost me a few birds. It ejects the spent shell, loads a new one but then firing pin isn't charged or cocked. So I pull the trigger and theres nothing there. Not really a mis fire because the it does nothing. I eject the shell, put it back in and I'm good to go. I hope I explained that right. I clean the gun regularly. Any ideas?
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Old January 26, 2014, 11:29 AM   #2
oneoldsap
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When you say you clean regularly , does that include the gas system ? Most new guns come from the factory with a good amount of crap in them . I always clean a new gun before firing it just for this reason . Generally when a gas operated gun isn't working just right , is dirty somewhere ! Your failure rate further reinforces this , as if it were mechanical , it would be occurring way more often , or constantly . Of course it's hard to diagnose without the gun in hand .
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Old January 26, 2014, 12:09 PM   #3
takem23
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I take it apart and clean the trigger assembly, piston and bolt assembly. I haven't taken the return spring and plunger out of the stock in a few years. I'll try that.
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Old January 26, 2014, 01:18 PM   #4
takem23
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cleaned the return spring and plunger. Wasn't very dirty. Cleaned everything with brake cleaner so we will see. Not sure how it could cycle a new shell without cocking that hammer/lever in the trigger assembly. Tried to replicate it manual but no luck.
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Old January 26, 2014, 03:42 PM   #5
g.willikers
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It may be cocking the hammer when it cycles, but the hammer may be not staying cocked.
It could be following the bolt forward.
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Old January 26, 2014, 04:57 PM   #6
takem23
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That sounds very possible. I wonder what causes that. Hammer not catching.
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Old January 26, 2014, 08:10 PM   #7
g.willikers
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It's hard to know long distance, like we have to do, but the sear might not have a firm grasp on the hammer between shots.
Or maybe the pins that hold the sear and/or the hammer in place are a little sloppy, allowing the slippage.
Or maybe a weak sear or trigger return spring.
But it's just a guess.
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Last edited by g.willikers; January 26, 2014 at 08:16 PM.
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Old January 26, 2014, 08:22 PM   #8
takem23
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Yeah I was thinking of replacing a few things if they weren't too expensive but can't find parts anywhere. Manual says it's for gunsmiths only.
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Old January 27, 2014, 06:29 AM   #9
Roughedge
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Take the trigger assembly out and cycle it a few times to see if it will do it out of the gun.
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Old January 27, 2014, 11:16 AM   #10
takem23
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I did try that. Couldn't get it to happen. Locked in nice every time.
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Old January 27, 2014, 04:56 PM   #11
Dixie Gunsmithing
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If its short-cycling, which would mean something up with the gas system, the bolt may not travel rearward enough to cock the hammer, and the hammer just follows the bolt closed. Is there any indent at all on the primer? I can't remember if that bolt has a firing pin block in it or not. Some do, so it won't go forward until the bolt is locked up, which would keep the primer from being deformed from a hammer following the bolt. My guess is short-cycling, and you might want to try it with other brands of ammo just to see what it does.
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Old January 27, 2014, 07:10 PM   #12
g.willikers
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Another thought is that recoil may cause the problem when it's not otherwise apparent.
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Old January 27, 2014, 07:58 PM   #13
takem23
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It happens with any type of shell. It might be short cycling but it is ejecting the shell and popping a new one in. I'm actually not sure if the primer is hit. I always reused it without checking. Since it doesn't click I didn't think to check.
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Old January 27, 2014, 08:41 PM   #14
takem23
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I never realized you can pop the rings off the piston. I'll clean that up real good. I spray it and scrub it buy It has a few thousand rounds through it.
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Old January 27, 2014, 09:37 PM   #15
Dixie Gunsmithing
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Check the primer on the next one that does it, if it does after cleaning. Even though it may eject, some bolts continue to move back as much as 1/2" after ejecting. Another possibility is wear on the hammer face, from the bolt riding on it, when camming it backward. If it were wore down enough, it might not catch the sear sometimes, if the bolt could not make it arc back enough. Though I would expect a lot of rounds through one for this to happen, but Mossberg has been known for using softer steel and castings in the past. A quick look at the hammer face, and the front body would tell.

The only other possibility would be a worn down firing pin, which might not indent a primer enough, if it was seated just a little lower than the rest. If not this, then check the hammer and gas system. However, you should be able to tell if the hammer followed the bolt forward when you cock it to throw out the misfired cartridge.

One last thing, clean out the gas port (hole) in the barrel. If it gets a little choked off, it can cause this too.
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Old January 28, 2014, 04:49 AM   #16
takem23
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Thanks. The hammer didn't appear to be worn but I'll double check. The gas ports are clear. Will I be able to visually tell if the firing pin is worn? I saw a video online to take it apart. Although the issue is hammer isn't getting cocked so I wouldn't suspect the firing pin. Unless I'm misunderstanding. I'll check it out.

Last edited by takem23; January 28, 2014 at 05:01 AM.
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Old January 28, 2014, 08:32 AM   #17
Dixie Gunsmithing
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No, I doubt its the firing pin. I threw that in as another cause if its not the hammer falling.

No, if the hammer is following the bolt forward, theres only a few things to cause this. Either the hammer is not being pushed back far enough to make it engage with the sear by the gas system (short-cycling), the sear notch on the hammer is starting to wear off, or the hammers camming surface against the bolt is worn away too much, but I would think you would have noticed it during takedown. If it seemed to work each time by hand, I doubt this being it.

If the gas port and the cylinder portion of the inside of the barrel ring are clean, suspect the seal ring on the piston. On Remington 1100's, the o-ring will look fine, but in reality, it is bad, and will short cycle. It's like this on the Mossberg 930 too, as it may look good, but it is possible it could be worn just enough to cause this since its intermittent. One last thing, make sure the two holes for the piston rods are not fouled up with dirt, as this might cause them to drag as they enter the receiver, and that the magazine tube, and inside of the piston are clean. Last, there is that forearm retainer that the rods pass through, make sure its not rubbing on the rods.
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Old January 28, 2014, 09:04 AM   #18
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Wow thanks for the help. You know your stuff. I'm sure I'll get now.
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