Mossberg 5500 MkII bolt carrier

[milktree]

Mine seems to have failed.

It's a piece of stamped steel with a piece of machined steel that fits into two notches in the stamped steel bit. It looks like the two are held together by four peened edges.

Mine was really loose. It looked like the peens had worn out/failed. and the cycling was starting to get rough.

So I took it out to the MIG welder and put a couple spots of silver Loctite (weld) on it to hold it together, nice and tight. It cycled perfectly, nice and smooth, lots of "dry" testing.

But when I went to do some doubles on Saturday the welds failed after 4 shots (all hits

I re-welded it yesterday, much bigger welds this time, but haven't had a chance to test it.

However it occurred to me that there might be some deliberate play between the two that I wasn't accounting for, and I never had a "new" one to look at (bought the gun used)

It *feels* right when the two are nice and tight, but a second opinion would be nice.

 

[KMM696]

I have one in the safe at home - I'll check tonight. I bought it new, but it's been a while since I've taken it out - can't remember if there's any deliberate play in that part.

 

[KMM696]

Checked my 5500, and that peened in piece on the action bar is solid, no play at all. Hopefully the larger welds will hold - that might be a difficult part to find.

Silver Loctite....I hadn't heard that one before. I like it.

Not a bad shotgun, perhaps not the best made. Too simple to break much, I think. Mine was my first shotgun, and it's certainly broke it's share of clays. The only failure I've had with it was the bolt handle detent notch wearing enough that it would come out way too easy. That just had to be cut a little deeper to fix it.

 

[milktree]

Checked my 5500, and that peened in piece on the action bar is solid, no play at all. Hopefully the larger welds will hold - that might be a difficult part to find.

Excellent, thanks. It confirms my expectation as to the way it should be.

here's my failed weld (first try)
http://mahonkin.com/~milktree/guns/5500/equipment_failure/med/is-61.JPG
http://mahonkin.com/~milktree/guns/5500/equipment_failure/med/should-be-60.JPG

and the fix (note much more weld, not just a spot)

http://mahonkin.com/~milktree/guns/5500/equipment_failure/med/fixed-63.jpg

It's kinda ugly, but it cycles smoothly so I don't think any of the ugly matters. That part of the bolt carrier only pushes the hammer back.

 

[KMM696]

Hope it holds up this time - let me know how it worked. The only thing I could think of that could be a problem with the first welds is how square the bolt face has to be to the chamber. Given the tolerances of the rest of the gun, I'm thinking it's probably pretty loose fit there. I'm not a welder, mind you, just a, well, aggressive tinkerer when it comes to guns.

 

[milktree]

Well, that was fun.... It worked... for about 40 rounds.

http://mahonkin.com/~milktree/guns/5500/equipment_failure/

I tried again, but this time I have more confidence in my work.

 

[ratman6]

So, what happened after your last weld? Did it Holdup? Thanks and so far loved your explanations and pics.

 

[milktree]

This time for sure!

http://mahonkin.com/~milktree/guns/5500/equipment_failure/

(more pictures, kinda the same)

short version:

It turns out that the bolt carrier is welded to the action bar, not just pinned. The two rectangular cutouts are there only for locating the carrier on the bar. The action bar has a hole drilled in it that's filled with weld to hold the carrier on, then the whole thing is ground flat and blued.

I'd been fixing the wrong thing.

After it started to crack and hang up again I took the whole thing apart, separated the carrier and action bar completely and found the echos of the hole drilled in the action bar to make the weld work.

This time I re-drilled the hole, cleaned up the carrier, cleaned up both locating holes, and welded all three.

It seems to have worked for 350+ rounds so far.

 

[KMM696]

Nice! Reminds me that I still haven't picked up a welder, either. Hope the carrier holds together this time - it would suck to have put this much time into a project an have it not work.