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Old 10-03-2019, 12:14 PM
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Any way to adjust head space on Model M pumps?



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I just noticed yesterday at the range that the cases have a slight buldege on the ends. Is there a way to adjust the head space. - Bill
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Old 10-03-2019, 01:34 PM
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haven't really thought about it as I have never had this issue, but the only way I can think of is cut and reset the barrel further in rcvr.

I have also seen some bolts worn, were the slide rod hooks in the side of the bolt. They were misshaped from excessive use, not allowing it to fully lock in as it should.

Sav22 also show another area to inspect for excessive wear in his write up.

Here is a picture I borrowed from the web, the area I was referring to is in the red circle.
[IMG][/IMG]
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Old 10-03-2019, 03:16 PM
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Thanks bone. I assumed it was either that or the lock-up directly above that. I was thinking to shim either one and seeing the results. The bulge is not very much and this won't get shot much. I have now got the tang peep sighted in at 25 yards by putting a piece of plastic bread bag tie under one side. The group was 5/8 inch deep, 3/8 inch wide with 3 shots in one hole just under the bulls eye. As I used parts from 2 guns to make this one I will just try to shim it. I do like this little pump and hope to find more.
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Old 10-03-2019, 06:11 PM
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Could it be just a bad chamber? If it is headspace and the problems is with the locking surfaces there might be a fix. I have a Mossberg Model S with what appears to be a repair to the locking surface in the receiver, I had posted pictures of this before but they are in photobucket and do not display correctly. I copied a couple of them & uploaded them here. It appears that a chisel was first used to move metal, that's what made the slightly angled cut, then it looks like a round punch was used to push the metal back into place to hold the bolt farther forward. I don't know how this could be done with out taking a chance of pushing it to far so that the bolt would not close. I had thoughts of taking an old bolt and cutting material away to somehow allow access to the locking surface with the bolt in place so the metal could be formed to fit the lugs.

I also edited in some more pictures to my recent thread on the Meriden/Mossberg pumps in the last post, I finally fixed he action lock on the late Model M. I used an old receiver half I had to make a cut-away to help with the fitting of the repair part. New Pictures

One of the new pictures that might apply here -


While I was in photobucket I also made a copy of a picture I had of bolt variations, you can see some distortion in the area Bone pointed on one of the bolts.

The Model S with what appears to be a repaired locking surface -
Attached Images
File Type: jpg Model S locking lug.jpg (115.7 KB, 2 views)
File Type: jpg bolt variations.jpg (282.9 KB, 2 views)

Last edited by Sav22; 10-03-2019 at 06:13 PM.
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Old 10-03-2019, 07:52 PM
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Hope you can see the issue.

Thanks for the replies. attaching a couple pics of the cases.



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Old 10-03-2019, 09:30 PM
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I really can't see much of anything in the pictures you posted. It looks like there might be a ring ahead of the rim but it's to far forward to be from head space issues - that would be just in front of the rim and you would need to have pictures of the cases setting on the rims to be able to see that. I think you may have a loose chamber, put some pieces of tape on the head of a cartridge and see if you can still close the bolt, if you can't it's not head space.
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Old 10-03-2019, 10:29 PM
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Thanks for the input Sav22. The second pic shows the raised end of the case just this side of the firing pin mark on the right one. The raised ends are not high but are noticeable. As the ejection is usually with some force I never noticed this until yesterdays shoot. I tried to eject without hitting the fellow next to me. After picking up the empties from the floor (behind him) he noticed the raised ends. The action appears to lock up tight but the cases have the raised end. I now realize I did not explain it correctly at first. The raised ends are not great but show under good light.
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