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Winchester Model 70 firing pin pitting
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Larned, Kansas
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April 29, 2023 - 5:46 pm
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Hi:

My first post in some time, so please forgive any protocol errors Embarassed:

I have two pre-War Model 70 rifles originally chambered for the .22 Hornet each with a pitted firing pin tip, one severe and one very slight; both guns are still functional.

Although I have owned multiple pre-1964 Model 70’s in “high pressure” calibers (.264 Win Mag for example), all post-War, since I have only owned these two M70’s in this caliber, I was wondering if this is a somewhat common experience (100% in my case) and what might be the cause?  Could it be the pin is too long and has pierced a primer causing “blowback” corrosion or something else.  Although I purchased each gun in a “used” condition, I have only used factory ammo in them. 

The gun with the very mild firing pin pit has been converted to .222 Remington Magnum by a former owner and is otherwise in 95% original condition (mfg. in 1937), while the gun with the extensive firing pin pitting is otherwise in very nice .98+% original condition (mfg. in 1941).

I hate to use either gun any further lest I cause further damage.

Many thanks for any input.

Mike Speers

mgs357

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April 29, 2023 - 10:24 pm
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I believe what you are seeing is erosion, nor corrosion. Typically this is a result of the hot gases escaping through a pierced primer. I have never experienced it in a model 70, but have seen it many times in high pressure varmint and target rounds. The Hornet is not usually considered a high pressure round but due to its small size, it is very easy to overcharge it and pierce primers as well as expand the primer pockets to the point where they will no longer seal or hold a primer. The 222 mag is a whole different animal and will definitely wreak havoc with primers. They don’t necessarily have to be overcharged either. I have experienced many instances with pierced primers that were very moderate loads but once the outside temp rises and the rifle becomes hot from shooting, the pressures will spike dramatically. Some powders are worse than others, of which some of the worst were the early ball powders. The newer powders such as Hodgdon’s line of “Extreme” powders have a deterrent coating that minimizes the problem a good deal, but will still be affected somewhat. One of the problems with the factory 70’s as well as Rem 700’s is the diameter of the firing pin and the clearance between the pin and bolt body. A smaller dia pin will withstand much more pressure w/o piercing due to the smaller surface area. 

     I cannot see your problem getting worse unless you experience more pierced primers.

Steve

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April 30, 2023 - 12:25 am
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Thanks Steve.

“Erosion” is probably a better word for what I experienced.

What I experienced was the firing pin occasionally piercing the primer and burning the tip of the pin.  I did some “memory refreshing” research and determined that the badly pitted firing pin is protruding too far out of the bolt face (0.066″).  Research into my old gunsmithing books reminded me that it should not extend more than 0.055″ which the very lightly pitted firing pin does.  To prevent any future problems, I will have to not only trim down the improper pin and polish it, I should also polish the “better” pin so as to give both pins a hemispherical mirror finish.  I have done this in the past, but it has now been over fifty years since I practiced gunsmithing and I had forgotten the proper “dimensions.”  With the badly deformed pin, I have plenty of “meat” left to correct the problem without shortening the pin too far.  The “better” pin will take only light polishing to correct it.

My original post was to see if anyone else had experienced the problem with other M70’s in .22 Hornet as I was surprised to see the only two pre-War Model 70’s I have owned to show the defect having never experienced it in another Winchester rifle in over 65 years of shooting them (I have many pre-War Winchester lever-actions and single-shots in various calibers). 

BTW: I would never have converted the Model 70 from .22 Hornet to any other caliber; I bot the .222 Rem Mag very reasonably for parts and have exchanged the firing pins to place the “good” pin in the very nice M70 Hornet; it is now a near perfect gun which I successfully tested this afternoon with no problems.

Many thanks for your input.Laugh

mgs357

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