What's happening with my 870? Locking block problem?

[alpining]

Hi all - I was just out doing some shooting on the weekend, and noticed what I think is a problem. This is an Express 18" that is about 15 years old. It has had a few hundred shells through it, with absolutely no problems until this weekend (except for poor extraction of crappy aluminum-based shotshells, of course).

Here's what happened: When firing some good quality 3" Winchester birdshot shells, the pump wound up about halfway back through its stroke during recoil. It's like the gun wanted to be semi auto, if you know what I mean. When this happened, it also would not feed the next shell out of the magazine - That same cycle of the action would fail to pop a round out of the mag, and I'd have to pump another full cycle to get one in the chamber. I'm pretty sure none of this had never happened before, so I broke it down to have a look at it and here's what I saw that worried me:

It looks like the locking block has shaved off the corner of the engagement surface on the barrel. Or perhaps that is normal wear. Can someone confirm whether or not this should be happening? The locking block itself looks okay to my eyes, maybe a little uneven wear, but it doesn't seem to match the wear on the barrel:

The action looked as clean as normal when I broke it down. 2 3/4 shells still work perfectly, and I'm pretty sure there were no issues when I ran some 3" slugs. Ejection of the hulls during the problem was fine, and the hulls look normal with no notable damage. They do have pretty flat primers in comparison with other hulls out of this gun, though (but I'm not sure on pressure signs for shotgun shells). I've stopped using this gun until I can confirm that it's safe to shoot again.

What do you think? Is the half-auto-pump malfunction related to the failure to feed? Caused by out-of-spec shells (hopefully!)? Or some kind of obstruction keeping the locking block from engaging perfectly? Manufacturing defect? I really appreciate any advice you can shoot my way...

 

[easy]

When the trigger is pulled, the action bar lock is sprung out of the way of the shell latch allowing a fresh shell to be released from the magazine tube.

Under recoil, after the action bar is unlocked, the fore-end and its assembly will travel rearward somewhat on its own if you're not holding onto it very well. That's a good thing. Many shooters anticipate that and use this to their advantage for faster cycling.

What happened to you is that when the action bars unlocked, the severity of the recoil and partly you not holding onto the fore-end very well, you did not cycle the action to the far-most rear of the stroke for another shell to be released from the magazine. The release of a shell from the magazine tube takes effect within the last 1/4" or so of the action stroke.

The barrel hood notch in your photo is a bit worn. Not sure if someone took a file to it, or not, but that area does get peened a little bit with use. More so if you're not manipulating the action with assertiveness.

 

[alpining]

When the trigger is pulled, the action bar lock is sprung out of the way of the shell latch allowing a fresh shell to be released from the magazine tube.

Under recoil, after the action bar is unlocked, the fore-end and its assembly will travel rearward somewhat on its own if you're not holding onto it very well. That's a good thing. Many shooters anticipate that and use this to their advantage for faster cycling.

What happened to you is that when the action bars unlocked, the severity of the recoil and partly you not holding onto the fore-end very well, you did not cycle the action to the far-most rear of the stroke for another shell to be released from the magazine. The release of a shell from the magazine tube takes effect within the last 1/4" or so of the action stroke.

The barrel hood notch in your photo is a bit worn. Not sure if someone took a file to it, or not, but that area does get peened a little bit with use. Excessively if you don't cycle the action assertively and to the fullest extent of its stroke.

Okay, so I guess I had a bit of a hypochondriac princess episode... I'm glad the problem was me, frankly.

I'm glad to hear that the wear on the 'barrel hood notch' (thanks for the correct vocabulary) is normal. It was definitely not filed, as I'm the original owner. I didn't know that weak racking could affect the lockup - I just assumed locked was locked.

While it's entirely possible, I'm a bit skeptical that I was short stroking the action and that's what was causing the failure to release a shell from the mag. I'm pretty careful about full travel, but I might well have been spooked by the unexpected slide travel under recoil. I can't be sure until I attempt to induce the problem again while shooting.

I do find it strange that it was only with the one kind of shell that I noticed the slide travel under recoil. Magnum 3" slugs didn't seem to do it, but 3" birdshot shells did. Different powder maybe, with a different "recoil profile". Or maybe I just happened to use a slightly looser grip and princess rack for that string of shots.

Thanks for the help, easy. I'm hoping to report back that you were entirely correct. Just as soon as I get out for another shooting session...

 

[alpining]

Resolved

I've heard back from both Remington warranty department and an independent Remington armorer about this. They both assure me it is typical wear and nothing to worry about.

Used this shotgun on the weekend with 100% reliability and no further surprises. I'm guessing the feeding problem was likely due to a thread of steel wool (or something similar) interfering with the shell stops.

Thanks again for the information posted to this thread.