FN 98 actions and fitting barrels

  • Thread starter Dennis Sorensen
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Dennis Sorensen

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Posted for general information...

A while back, I can not find the thread (possibly it is deleted), the subject of the inner ring in 98 actions was discussed. One of the reasons Mauser designed this ring was for gas handling abilities. This has been established by old published data. It was a stated design feature. I have referred to this ring as a headspace ring. Some are open on one raceway only, some are open on both raceways. This early commercial FN is open on both raceways.

At that time I felt the bigger purpose was to fit barrels against it. Although I have not seen any data from Mauser stating this I still feel that is a primary reason for it. Many, many factory fitted barrels both military and commercial had barrels with not enough shoulder diameter to use the shoulder as a stop against the action. The barrel had to be fitted against that "headspace ring". I have also found headspace measurements are extremely consistent if you measure from that ring to the bolt face on un-altered actions.

This picture is of an old commercial FN 98 30-06 serial number 6780. The barrel diameter is 1.100", the same diameter as the threads. This supports my thoughts about this 'inner ring'

fnaction-0.jpg
 
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Dennis,

On a minor point, I recall reading somewhere that Mauser designed the ring with a single cutout for the extractor & some subsequent factories cut the second as a manufacturing expedient.

John
 
Butch Lambert said:
Dennis,
Buddy, I think you are beating a dead horse.
Butch
Click to expand...

I guess it could be perceived that way but it is not my intent to beat anything... nor to rile anyone. :)

I just feel there is more purpose to the inner ring than simply a gas handling feature... out of hundreds of unaltered 98 actions I have measured, the headspace measurement from the front of the inner ring to the bolt face was consistently from .106" to .108". This allows mass production of chambered barrels that will headspace correctly with no fitting to an individual action. Sights are simply added after the chambered barrel is snapped on tight. The barrel diameter ahead of the action was intentionally the same diameter as the threads so there was no "shoulder' to interfere with the fit of the barrel into the action. Later larger diameter barrels were fitted but the barrel was still correctly fitted against the inner ring.

Mauser stated the intent of the ring was for gas control but whether it was intentional or coincidence this inner ring is also very useful in headspacing and was neccessary to fit the small diameter barrels. It does serve more purpose than just gas control... and as far as anyone today fitting a barrel to a 98, the purpose of the inner ring is to fit the barrel against it...

just my thoughts...
 
The Enfield actions also have this sort of bulkhead. When a barrel is fitted properly it should torque down evenly against both the receiver ring and the bulkhead.
When examining a Lithgow No.1 action with barrel removed I found that the inner surface of the bulkhead was not flat. The center was a good deal further forward than the rest of it.
I believe that would allow a longer shank to butt against the center which would then be pushed back as the barrel was cranked tight.
Worn Enfields with looser than usual, and they are almost all a bit loose, often show a gap between the barrel breech and the bulkhead. I suspect this is a sign they'd been rebarreled before, perhaps several times. The center of the bulkhead permanently deformed.

Because the Enfield barrel must be clocked in to match up the extractor cut and sight bed they used boltheads of varying lengths to achieve proper headspace.
 
I hope I don't add to beating this horse to death but would someone explain to me how in the hell that inner ring contains the gas? I mean the bolt fits up close, within about .105" of the barrel face and into the bore of that ring. No "three rings of steel here"

Also Dennis, when measuring from the inner ring to the bolt face, how is that done? doesn't the outer action face get in the way of the depth mike? When I have measure more than a few Mausers, the dimension from the receiver face to the inner ring can vary as much as .008" at different points around the face. I don't think I have seen a receiver face that is parallel to the inner ring yet.
 
Jkob said:
I hope I don't add to beating this horse to death but would someone explain to me how in the hell that inner ring contains the gas? I mean the bolt fits up close, within about .105" of the barrel face and into the bore of that ring. No "three rings of steel here"

Also Dennis, when measuring from the inner ring to the bolt face, how is that done? doesn't the outer action face get in the way of the depth mike? When I have measure more than a few Mausers, the dimension from the receiver face to the inner ring can vary as much as .008" at different points around the face. I don't think I have seen a receiver face that is parallel to the inner ring yet.
Click to expand...

It in no way contains gas as some more modern designs do but it does add some strength to the action over previous designs in the 1800's.

Turn a piece of steel to be about .800" round, make it exactly .800" long with machined true ends and drill a 3/8" hole lengthwise. This piece can be placed on the inner ring and a depth mike to the bolt face. Measure around the bolt face not just on the firing pin hole. The .106" to .108" measurement you will probably get is confirmed when the barrel is fitted and checked with a steel go gauge.
 
Good one, I will have to try that. Now why didn't I think of that? I use a couple of different sized "tubes" that fit over the barrel threads to measure headspace in almost the same way.
 
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