Forend retract

[lester251]

Hi, first post here, but I have my remington 870 super mag for more than 2 years, I was looking for an answer but couldn't find anything to help me.

Everytime I shoot 3 inch or 3 1/2 steel shell, the forend doesn't stay in place and retract backward a few inches. It does the same time as if I would reload a new shell but partially. I don't have any problem shooting 2 3/4 lead shell. The shell doesn't eject,

I joinded I picture took a second after I shot.

Hope you guys can help,
thank you very much

edit: sorry for the image size, didn'T realise it was that big!

[Kentactic]

If its coming back that far it cant be right. Shoot it with only your strong side hand. See if the action moves back then with no contact on the forend.

[blackwatch42nd]

Hi Guys, New to posting here but have a friend who has the same problem but with any shell length in his 870. Sometimes the forend retracts after a shot even if there is no contact on the forend. Also if you continue the extraction it won't feed the next shell. you have to close the chamber then release the slide and pump the action again.
Any ideas.
Thanx
John

[lester251]

I called remington to have some information on that problem,

The gunsmith told me to do a simple test,
While having your gun secure and unloaded, take a meteal rod or your cleaning rod and push on the bolt action from the barrel,
While keeping the pressure do a dry shot
After the dry shot and keeping the pressure on the bolt action if the forend doens't retract then the gun is safe
If you release the pressure and put pressure back (and slighty move the receiver) then the gun is safe

That mean that it is the pressure coming back from the barel that retract the forend and not the inital explosion, the gunsmith told me it might be usure from the receiver that can cause this or a too narow choke.

I will try to use smaller load or wider choke, changing the receiver isn'T worth the money for me on a +5 years old gun.

[Synchronizor]

Here's a basic explanation of how the bolt lock-up works on a properly-functioning 870:

This image has some minor inaccuracies relating to part design, but it accurately illustrates the general mechanics of the 870's action.

870 action F4.jpg (75.1 KiB) Viewed 4851 times

The 870's breech bolt assembly contains a moving locking block that lifts up to engage the barrel when the gun is in battery, and drops down to disengage from the barrel when the action is opened. The locking block is actuated by the movement of the slide assembly (the part that the bolt rides on) inside the bolt. If you take your gun apart and place the bolt onto the slide assembly, you can see the locking block move up and down as you slide the bolt back and forth on the slide assembly.

When the gun is assembled, the slide assembly moves with the action bars and fore-end. When the hammer is cocked and the fore-end is all the way forward, the slide assembly is forward in the bolt, keeping the locking block raised and locked into the barrel, and the action bar lock in the trigger plate assembly engages the end of one of the action bars to keep the fore-end assembly where it is, holding everything in battery. As soon as the trigger is pulled and the hammer is released, the action bar lock drops down, freeing the action bar and allowing the fore-end to be brought back to cycle the gun. But the bolt itself will not unlock from the barrel and start moving rearward until the fore-end and slide assembly move back far enough for the locking block to tilt down and unlock the breech. You can see the slide assembly, bolt, and locking block if you look through the ejection port, and watch them operate as you dry-fire and cycle the gun.



Now, if I managed to explain all that well enough (and let me know if anything confused you), you hopefully should be able to understand that until the fore-end is directly moved backward, no amount of force on the closed breechface should cause the action to open, even if the trigger has been pulled and the action bar lock is disengaged. This is what you're testing when you press or tap on the closed breechface with a dowel or cleaning rod. If you can force the action open without touching the fore-end or allowing it to slip backward due to gravity or inertia (if necessary, use a small rubber band to keep it from slipping backward), then there's something wrong with your gun - likely wear or damage to the locking block and/or the locking notch in the barrel - and you shouldn't fire anything in it until you can get the problem fixed. But if you can't force the action open (and don't be afraid to push hard, a 3.5" 12ga shell can generate up to 14,000 psi of pressure), then you should be fine.

If there's nothing wrong with the bolt lock-up, my best guess is that the recoil of those very heavy loads is transferring enough momentum to the gun for the fore-end & slide to keep moving and unlock after your shoulder stops the rearward movement of the rest of the gun. Try firing the gun in a solid rest, or with the butt braced against a sturdy tree or post. If it is the recoil-induced movement of the gun that's causing the bolt to unlock, it should stop if the gun is completely immobilized.

That mean that it is the pressure coming back from the barel that retract the forend and not the inital explosion, the gunsmith told me it might be usure from the receiver that can cause this or a too narow choke.

I will try to use smaller load or wider choke, changing the receiver isn'T worth the money for me on a +5 years old gun.

I'm not quite sure what you mean there, but you may be misunderstanding what was said. The bolt locks directly into the barrel in an 870, not the receiver; and as I explained, no amount of (normal) chamber or barrel pressure should be able to unlock the bolt directly, whether it's the high pressure of the initial firing or some sort of reflected pressure wave from the choke.