870 malfunction. Help me with diagnosis.

[Correia]

Ok 870 fans, I need a bit of help.

Shooting an 870 in a match today, I got a surprise click and no boom. Happened a few more times. Really screwed my overall time!

Here is what is happening. Sometimes when I pump, no new shell is popping out of the mag tube. I pump air, and end up dryfiring at the target.

I had somebody watch me to make sure that I was not short stroking the gun. No problem. Good solid full hit to the rear, full hit forward. Not the problem.

I think that it may be something to do with the little claws that hold the shells in. However when I look at them they seem to be fine. Nice and springy.

This only happened when shooting fast. I could not get it to happen while shooting slow.

Any ideas? What are some things I can look for?

Note, this 870 has been in continuous hard core use since the late 1980s. And when I say hard core, I ain't talking coming out of the closet during duck season. Not sure, but probably around 100K rounds at this point. (one of the other competitors told me I needed to retire the old gun and get something new. I told him to go perform certain unnatural acts on livestock.)

 

[DML]

When was the last time you cleaned the inside of the magazine tube?

Without seeing the gun, diagnosis can be difficult, but my guess is that the magazine spring and/or follower is hanging up in the magazine tube. I would try cleaning the inside of the tube very well and see if there is any crud on the follower. Also check the spring for kinks and replace it if it doesn't look right.

Since you said that you don't have the problem when working the action slowly, it sure sounds like a problem inside the magazine tube.

 

[Preacherman]

I concur with DML: since this is happening only during high-speed operation, it sounds to me like a magazine tube problem rather than a shell-stop or shell-lifter problem.

A few questions:

1. What length mag tube (including extension) do you have? Is the spring in the magazine strong enough to cope with that length even under high-speed operation, or is it a bit weak, so that it exerts sufficient pressure to move a round at slower speeds, but can't move it fast enough during a high-speed reload? I know one guy who uses a spring designed for a 10-round magazine in his 8-round extended mag: it's heavy, and hard to load the last round, but he prefers the extra strength in the spring for high-speed operation. (Oh, BTW - when was the spring last replaced?)

2. Have you checked out the joint between the factory mag tube and the extension? If the latter is removed and replaced often enough (e.g. with intensive cleaning), I've seen a couple of cases where burrs developed at the joint, sufficient to cause the mag spring to "hang up" momentarily on the burr. In high-speed operation, this brief hang-up might be sufficient to cause the malfunction you describe.

3. What about the mag follower? If it's one of the plastic units, these can become scarred and burred over time by contact with the shell-stops and with the aforementioned burrs between mag extension tube and original mag tube.

4. When did you last deep-clean the mag tube?

HTH...

 

[9mmMike]

I will third the mag spring and/or follower. I have a gaggle of 870's here and I am always loaning them out. The last time we had a large group of folks shooting, one of my loaners had the same problem. It turned out to be a mag spring that had somehow managed to slip around a follower and was binding in the tube. The spring had an end that was not well-coiled and normally went in towards the cap but had been installed towards the follower instead. It scored the heck out of my mag tube and slowed the shell loading enough to load some "air". Check the follower and the spring and you might wish to check the tube for rust or gunk build-up.
Good luck,
Mike

 

[Coronach]

The mag spring in my cruiser gun would sometimes bind at times, causing the exact same effect. When you load the shells, do they slide in steadily, with a uniform feel? Or do one or two seem obviously 'harder' to load than the rest (ignoring steady increase in pressure as the mag fills up)? If so, that might be the problem. You could also hear the spring catching on something as you loaded it....though I didn't notice the difference in sound until the gnomes out at ordnance fixed it.

Mike

 

[Correia]

Good points all. I had not thought of that. I will check out the mag tube and see if there may be a problem. It has been awhile since I did a good cleaning of the mag tube. I have a 2 shot extension and the regular spring for that. That spring has been inplace for about a year. I will check it, replace if neccesary. The follower is metal.

Due to my suspicions about the shell holders I went over them real well last night. The left one does not appear to be functioning. When I played with it before I posted last night It felt fine because it was still springy. However when I went over it after I posted I found that it is stuck to far down. It does not hold the shell at all. Only the right one is working. Not that that would explain shells not feeding out of the tube, but I'm glad I caught it before it became a problem.

 

[Andrew Wyatt]

check the interruptor latches for burrs, too.


replacing the broken one is probably in order.

 

[kotengu]

Man what a POS - I knew 870's weren't worth ****. Only 100,000 rounds and it fails to feed every once in awhile......

 

[Correia]

Yep, POS. Going to go chuck it in the river right now!

Anybody know how to replace the latch? I've never taken those out before?

 

[Andrew Wyatt]

One of the weaknesses of the 870 in my opinion are the staked on shell latches. of course, with the 500 series, the shell latches come out whether you want them to or not every time you dissassemble the gun.


It's pretty much a gunsmith deal unless you get the appropriate tool and have 1337 sk1llz, D00D.