Give it to me straight, doc (870 malfunction?)

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BBroadside

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Today I shot two rounds of skeet. So my Remington 870 Express 12-gauge digested 50 rounds of #8 no problem.

Then I decided to try out the new slug barrel I got and the five rounds of Brenneke K.O. slugs. First shot, and the action opened by itself. My 870 thought she was an autoloader for a second. In an admittedly dumb move, I fired off the other four rounds (edit: all slugs) with no further odd behavior. (Accuracy was not bad, incidentally.)

As I was driving home, I decided I was a complete numbskull for having shot the last four rounds. Now the questions is - what exactly happened?

Was this some sort of an anomaly from not having closed the action properly in the first place, i.e., the weapon is still shootable if the shooter is reliable? I wouldn't expect a pump shotgun to fire out of battery but I suppose stranger things have happened.

Or has some part gotten tweaked in a way that makes it iffy for the action to stay closed? Should I pull it apart and look from something bent/broken?
 
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This is normal. The action will open with light loads also if your not holding it closed with your hand on the forearm. You probably just noticed because of the stouter loaded slugs. No worries.
 
+1 Cypress.
As an experiment next time you have 870 out fire it with one hand. it should shuck itself if you don't move to much from the recoil.
 
Oh I get it. So a nice light load (like my first 50 rounds) doesn't require too tight a grip on the forend to keep the action shut, but the slugs (which kicked about as hard as everyone says, so I wasn't surprised) are a different matter. Having the action open on its own probably rattled me enough that I had a death grip on the forend for the last four slugs.

For some reason, I though this only happened with the old Winchester 1200 and 1300s that USRAC used to make (or still makes).

I am very pleasantly surprised. My 870 was very inexpensive but it has been utterly reliable up to now; I'm very happy with it. Now I have to adjust the sights. My pattern was to the right of the bullseye, so either I have to move the front sight left, or the rear right to the right. (It's a Wingmaster 20" rifle-sighted, RemChoke.) I'll figure it out.
 
Your shoulder went back more when you shot the slug. This means it went forward more when you recovered and since you were holding the forearm it opened the action. You were ready for the rest of the slugs and didn't move as much with the recoil.

Just my theory...
 
The 870 is designed so that the forearm has to move forward a bit (as it will in recoil, when the rest of the gun moves back) before it will unlock for the action to open. There's nothing wrong with your 870 - just the difference in recoil levels of the two rounds.

Try pulling the forearm firmly to the rear next time you shoot light birdshot loads, preferably at a stationary target on the flat range. Until you bump the forearm forward a fraction of an inch, the action won't unlock... (ETA: if the gun is functioning properly, that is)

lpl
 
It may have recoiled more than you expected and you may have pumped in the act of regaining your balance or if you rolled with the recoil.

In some circumstances, it's possible for pump handle to have enough momentum upon recoil to open itself. Kind of like a primitive inertia action.

Firing out of battery is very bad. If it did, you would definitely know it.
 
Probably had to do with how you were holding the shotgun. Think about it: under recoil, everything moves back, but when your shoulder "comes back," if you're not holding the foreend well, the foreend is now unlocked and can move. The shotgun moves forward, while relatively, the foreend does not. It'll come open a bit.

The same effect appears when you shoot a pump shotgun on a bench with the foreend on a bag.
 
LeeLapin, I said that same thing,post 7, two weeks ago on a different thread, Thank You.

Dog piled was an exageration,went back and found the thread it wasn't as bad as I remembered.
 
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Sounds like you may want to check it out a little further, Broadside. The design should allow unlocking with forward resistance on the forearm, and it sounds like yours unlocked itself under inertia alone...which it's not supposed to do...essentially letting the bolt function like a straight blowback with the barrel still under pressure. Bad JuJu no matter how ya cut it.

Test it by firing the gun with one hand with low brass field loads to see if it'll do it again...and keep the port angled slightly toward the ground. If it does...get thee to a pumpgun wrench.
 
It's easy enough to test the function of the action bar lock without actually shooting the shotgun at all, and is probably a better diagnostic than doing the test live fire, with recoil to try and counteract while performing the test. Triple check to be sure the gun is clear, especially the chamber (look AND feel), point the muzzle in a safe direction, pull back firmly on the forearm, and trip the trigger while still pulling back firmly on the forearm. DO NOT OVERLOOK CLEARING THE CHAMBER AND MAGAZINE BEFORE DOING THIS. DO NOT FAIL TO POINT THE MUZZLE IN A SAFE DIRECTION WHEN PERFORMING THIS FUNCTION TEST. A casual approach to doing stuff like this leads to BOOMS not clicks. If you cannot be absolutely safe in clearing the gun completely and exercising muzzle control, don't do this test at all.

A properly functioning 870 will stay locked up after the hammer falls, until you push the forearm forward a fraction of an inch to unlock it. With an older and slicker 870, it may be only a tiny fraction of an inch, but if the forearm is firmly held back when the trigger is pulled, the action should stay locked after hammerfall until the forearm is moved forward a tiny bit. There should be a loud CLICK when the hammer falls, and a softer click (may not even be audible on some guns) when the action unlocks after the forearm is moved forward a bit.

If the forearm unlocks instantly under these conditions without the forearm being moved forward at all, the gun needs help from a 'smith. I prefer to do this test outside, seated, with the butt of the cleared and checked shotgun sitting on my knee/thigh to give firm resistance to push the forearm back against.

Take a look at http://www.urban-armory.com/diagrams/rem870.htm . The upwardly extended tab on Part #1 in the drawing is pretty much all that is keeping the action locked closed when the gun fires, and it's possible for it to wear to the point of failure over time, or for it to be bent/damaged/misaligned by forcing the forearm back too hard when the action is locked or by careless and overly forceful reassembly of the trigger plate assembly. That's why I said FIRMLY and not GORILLA GRIP when describing pulling the forearm back before tripping the trigger to test this function with an empty gun.

Safety First, Last And Always,

lpl
 
Lee Lapin, I assume this test will work with snap caps, is that right? I have some of those, so that would be my first choice for trying this.
 
Yeah, snap caps are the all-green plastic ones with the brass bases ... DOH!!

Actually, the maroon color of the A-Zooms was well chosen. Never seen a real shell that color. 'Course, the A-Zooms are all metal too, so I could tell in the dark. Not that I'd have too.

I am pleased by your attention to safety, Mista Lapin.
 
From Remington's Support site:

http://remington.custhelp.com/app/answers/detail/a_id/87/kw/870/r_id/166

This has been discussed numerous times. It is perfectly normal. If you fire the gun without touching the fore end it will open every time. Even with light loads. My well worn 870 will almost eject the shell.

This was demonstrated at a shotgun class that I took a few years ago. Give it a try, any 870 without touching the fore end will open when fired. The charge is long gone, so there is no danger, and it is not a malfunction.
 
Well, I'm glad I started this thread, because I subjected my 870 Express to the test specified by Lee Lapin ... and it failed. A gentle pull back on the forearm causes it to be released backwards immediately when the trigger is pulled, whether or not I'm using snap caps.

Boo. Guess I need to find a good gunsmith.
 
Check out Snarlington's link. It's a real genuine Remington factory link.

Read what it says, and even contact Remington yourself to verify.
Even with the test you conducted, your shotgun may be normal and safe.
 
As soon as the trigger is pulled and the hammer falls, the bolt and fore end are unlocked. What is so hard to understand about this? That is exactly how it is supposed to work.
If you are pulling back hard, and the force of your pull is not overcome by recoil, it is likely the friction generated between the locking block and the barrel extension will not allow the fore end to move. Under recoil, the bolt will not come back until the pressure has dropped and the shot is long gone. If you are pulling back gently after dropping the hammer on an empty chamber or a snap cap, it should move to the rear as soon as the hammer has dropped. You do not need a gunsmith. What you need to do is pay attention.
 
Once upon a time, someone perceived the persistence of the action bar lock remaining engaged in the face of rearward pressure on the forearm when the trigger was pulled as a problem, and reported it here as such - http://www.thehighroad.org/archive/index.php/t-545184.html .

The bevel on the front of the action bar lock engages a similarly angled bevel at the rear of the left action bar. It is this engagement which keeps the action locked during firing. Under normal circumstances when the gun is fired, the forearm is moved forward sufficiently in relation to the rest of the gun (which is being moved backward by recoil) to unlock the action. On a smoothly functioning 870, any degree of forward movement in the forearm - even if it is not perceptible to the shooter - will unlock the action, as it should. That is why the action seems to release the instant the gun is fired, and why the bolt will retract to some degree even if there is no hand on the forearm at all. It's not humanly possible to perceive what is going on because it happens too fast.

Take your assembled, unloaded 870, action closed and on safe, to a place where you have good light. Push up the lifter, and look inside the receiver on the left side, where the action release is located. You can see where the front bevel of the action bar lock engages the rear bevel of the left action bar. If the action bar lock is misaligned/bent/damaged/worn, there is a good possibility you can see this problem with the parts (action bar lock and left action bar) in relative position to each other.

These are among the parts that help make certain the bolt does not blow open instantly and forcefully upon firing (a condition known as failure to hold action lock), as it would if there were some problem with these and/or other parts. As Kuhnhausen'e shop manual for the 870 puts it (page 59 in my copy):

The action bar lock is critical because it operates as the timing link between the action bar/slide/breech bolt group and the fire control assy. [sic] The action bar lock is cycled and timed by the rear bevel and the steps in the bottom of the left action bar.​

hth,

lpl
 
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