870 problems

brandan · November 6, 2014, 06:22 PM

I have a 870 express 12 gauge that after I fire it the action opens about a 1/2 or so on its own, I noticed it when I was shooting it with a pistol grip one handed so I know it not just my arm moving. I did install a ATI tactical fore end but have no clue if it was doing it before that or not, I cant seem to find any info anywhere online about what could be wrong, any help would be appreciated. thanks in advance

Sharkbite · November 6, 2014, 06:47 PM

With heavy recoiling loads this can happen. The action is unlocked as soon as the trigger is tripped. Recoil happens after this and with a stout load the action will open a little.

Crazy88Fingers · November 6, 2014, 06:50 PM

Completely normal. Can even aid in quicker reloads if you're super high speed.

brandan · November 6, 2014, 07:00 PM

it does it with low recoil rounds to, I read that it was normal on another type of shotgun I just didn't know about the 870 so I figured id ask before damaging my gun

yadkin · November 6, 2014, 07:05 PM

Yep it happens, my 870 tactical does the same when I shoot it off the bench when zeroing slugs, I have a mossburg 500 that if you dont hold the fore grip it will completely eject the round due to heavy recoil.

**4V50 Gary** · November 6, 2014, 07:09 PM

Yadkin - can you force the slide back if the trigger isn't dropped? I worked on a 410 cal Mossberg 500 that did that. I sent the bolt slide back to Maverick Arms in TX (Mossberg told me to send it there) for exchange. The new one worked fine.

Dixie Gunsmithing · November 6, 2014, 07:31 PM

It happens only while you are not holding the forearm, does it not?

Holding the forearm is required, if there is no spring to keep tension on the forearm, as in the 870, with the bolt closed and fired. Friction is what keeps the action bar lock from being actuated after firing, and that friction comes from the shooter holding the forearm on these guns. The action bar lock contacts the action slide under the bolt. When you hold the forearm, while shooting, it produces a friction from the recoil between the lock and the slide. When you start to pump the gun, the friction is released. During firing, the hammer falling puts tension on the action bar lock, via a spring, which will make it drop down from the action slide, so the gun can be pumped, after the rearward forearm pressure is released.

Winchester Model 12's, and the Mossberg pumps, use a spring on the magazine tube, so one can fire them without holding the forearm. Remington 870's don't have this.

If a Mossberg does this, something is wrong.

brandan · November 6, 2014, 07:46 PM

thanks for the answers

November 6, 2014, 06:22 PM	#1
brandan Junior Member Join Date: September 22, 2014 Posts: 6	870 problems I have a 870 express 12 gauge that after I fire it the action opens about a 1/2 or so on its own, I noticed it when I was shooting it with a pistol grip one handed so I know it not just my arm moving. I did install a ATI tactical fore end but have no clue if it was doing it before that or not, I cant seem to find any info anywhere online about what could be wrong, any help would be appreciated. thanks in advance

November 6, 2014, 07:09 PM	#6
4V50 Gary Staff Join Date: November 2, 1998 Location: Colorado Posts: 21,833	Yadkin - can you force the slide back if the trigger isn't dropped? I worked on a 410 cal Mossberg 500 that did that. I sent the bolt slide back to Maverick Arms in TX (Mossberg told me to send it there) for exchange. The new one worked fine. __________________ Vigilantibus et non dormientibus jura subveniunt. *Molon Labe!*

November 6, 2014, 06:47 PM	#2
Sharkbite Senior Member Join Date: November 4, 2013 Location: Western slope of Colorado Posts: 3,679	With heavy recoiling loads this can happen. The action is unlocked as soon as the trigger is tripped. Recoil happens after this and with a stout load the action will open a little.

November 6, 2014, 06:50 PM	#3
Crazy88Fingers Senior Member Join Date: November 20, 2010 Location: WesTex Posts: 958	Completely normal. Can even aid in quicker reloads if you're super high speed.

November 6, 2014, 07:00 PM	#4
brandan Junior Member Join Date: September 22, 2014 Posts: 6	it does it with low recoil rounds to, I read that it was normal on another type of shotgun I just didn't know about the 870 so I figured id ask before damaging my gun

November 6, 2014, 07:05 PM	#5
yadkin Member Join Date: September 21, 2012 Location: North Alabama The Heart o Posts: 32	Yep it happens, my 870 tactical does the same when I shoot it off the bench when zeroing slugs, I have a mossburg 500 that if you dont hold the fore grip it will completely eject the round due to heavy recoil.

November 6, 2014, 07:31 PM	#7
Dixie Gunsmithing Moderator Emeritus Join Date: April 27, 2013 Location: Ohio Posts: 1,923	It happens only while you are not holding the forearm, does it not? Holding the forearm is required, if there is no spring to keep tension on the forearm, as in the 870, with the bolt closed and fired. Friction is what keeps the action bar lock from being actuated after firing, and that friction comes from the shooter holding the forearm on these guns. The action bar lock contacts the action slide under the bolt. When you hold the forearm, while shooting, it produces a friction from the recoil between the lock and the slide. When you start to pump the gun, the friction is released. During firing, the hammer falling puts tension on the action bar lock, via a spring, which will make it drop down from the action slide, so the gun can be pumped, after the rearward forearm pressure is released. Winchester Model 12's, and the Mossberg pumps, use a spring on the magazine tube, so one can fire them without holding the forearm. Remington 870's don't have this. If a Mossberg does this, something is wrong.

November 6, 2014, 07:46 PM	#8
brandan Junior Member Join Date: September 22, 2014 Posts: 6	thanks for the answers