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Discussion Starter · #1 ·
I have a M12, 16ga that the firing pin strikes off center on the primer. This causes misfires at times.

The headspace is tight, the firing pin extends 0.060 from the front of the bolt, and the hammer spring has been replaced and is strong. The gun is a newer 1955 model and has seen little use.

I did at one time have a problem with the left hand extractor contacting the rim on a chambered shell when closing the bolt; I corrected this by reshaping the left extractor a little, and reducing the spring tension on the right hand extractor. Now I am wondering if the bolt is closing a little cocked and this was causing the above problem along with the firing pin strikes being off center.

Has anyone had a problem like this? This gun has the flat bottom bolt and not the older round bottom and the bolt is right up where it should be when closed (cannot see firing pin retractor), I was thinking of removing a little metal on one of the respective lower lugs to get the bolt to tip up straight or should I just live with it?
 

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Hello James: don't do it. The firing pin is not off center!! The barrel chamber ring and the barrel relationship is off center in relation ship to the bolt. The barrel chamber ring is "reamed" to match the barrel chamber. This is where your problem lies.

Most off all my Md 12s don't strike the primer dead center always off a little. If yours is so far off it's causing misfires then someone has messed with the barrel chamber ring in front of the bolt.

Regards Dave
 

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Discussion Starter · #3 ·
Thanks for your reply 'Only Winchesters'

Yes the chamber ring was changed by myself because I was having a lot misfires. I measured the headspace at something like 0.040", the firing pin still hit off center before I changed the ring. It was cut undersized on a lathe to the original and fitted carefully with a half round file to match the chamber. I did not counter bore the face and headspace is under 0.010" now.

At the same time I installed a new hammer spring. Misfires now are rare and only with remington factory game loads that I reload. When I am using Winchester primers I seem to have no problems.

I think you are right and I will leave well enough alone. I have 4 other M12's and this is the only one I have had a lot of trouble with the others have alway been perfect.
 

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What direction is the firing pin dent shifted from center?
Extractor balance of spring pressure, plus tip dimensions, all can influence where the bolt face sits when closed.
A firing pin that is slightly off-center is typical and normal on many models of guns, but not all have as much side play room as the M-12 bolt face.
If the extractor tip size causes extra pressure on one side (and may be due to something about the extractor slots, too) and the other side has a weak spring, a natural pull to the one side is understandable.
This situation is much more prevalent than an off-center chamber in a barrel, but Dave remembers the situation that I explained about the off-center manufactured adjusting sleeves that would mimic a problematic barrel.

The real mystery is why the "original" chamber ring had such egregious headspace gapping, since that is near the level where the firing pin is unable to reach a normally seated primer that is below flush (as it should be) in the head.

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Discussion Starter · #5 ·
Thanks Kirby for your help.

The bolt should go to the right a little to improve the firing pin impact area. I did have to cut the left hand extractor spring to let it move it that direction. But I did not give a lot of though to this balance and the shape and fitting of the extactors. Some day when I have some time I will have another look at it and see if an improvement can be made.

As far as the headspace I have no idea why it was so bad. I have seen this only on guns that have been shot a great deal. There was no indication of wear or peening of the lug area on this gun. I do not ever want to fit another chamber ring it is a lot of work but had to be done in this case. It is a job for a good gunsmith that know this model.

I will keep in touch if I find anything.
 

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James: there is one more thing you might want to check. If the firing pin was replaced at some point. there's a chance that the tip was ground off center. Or when the firing pin was fit, so it wouldn't protrude to far, (puncture primers) the tip could have been (filed, ground, etc.) off center.

Pretty easy check to look at the bolt face while pushing the back of the pin so it can protrude. It might be as simple as putting in a new firing pin.

Regards Dave
 
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