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mauser rifle threads

slidewaysslideways Member Posts: 9 ✭✭
edited May 2010 in Ask the Experts
G'Morning, I acquired a Czech VZ-24 minus the receiver and thought that I would use a 1938 FNC receiver that I had. Both 8mm, the barrels are the same length, steps, and the threads appear to be the same. (They lay in each other.)The Czech barrel seems to thread bind a little more than 1 turn into the FN receiver, while the wore out FN barrel screws in all but about 3/4 turn by hand. The FN barrel threads appear to have been filed into a bit of an acme thread and there are four home butchered self tapping notches filed 90 degrees apart into them (the threads). It seems too loose in its threads till it bottoms. FN receiver and barrel are/were number matched. The reciever threads appear undamaged. The VZ barrel is stamped VZ24 8mm CZECHO, CAI ST ALB VT., K2, B4, 6108, an inverted V and what looks like a lion stamp. The threads on it appear to be unmolested, it's rifling is good and it's reasonably blue-black. I still have to round up the proper tightening tools, but feel like I may be at a "a little knowledge is dangerous" stage. What am I missing? Thank you.

Comments

  • 260260 Member Posts: 1,134
    edited November -1
    you might get a thread pitch gauge and check both.
    i have had to remove barrels that were so tight that i had to use a 4ft. cheater pipe on the action wrench. it's the nature of the beast at times. if it gauges ok, use some assembly paste when you screw her down and don't forget to check the head space.
  • nononsensenononsense Member, Moderator Posts: 10,536 ******
    edited November -1
    slideways.

    There have been a dozen or more manufacturers of the Mauser M98 pattern actions and rifles. As closely controlled as the processes were, there was always the possibility that small variations could occur. This is never more noticeable than with a thread form. Given the huge quantities of M98 rifles manufactured, the number of problem fits is extremely small but they can happen.

    The Mauser M98 large ring thread was 1.1"- 55 degrees as opposed to our standard thread form of 60 degrees.

    Sometimes oxidation, minor imperfections (dings) or tiny changes (wear, chips) in cutting tools resulted in barrels that are slightly tighter than necessary for a proper fit. Under wartime conditions, this was ignored in favor of productions numbers so the barrels were simply forced on.

    All this means is that not even the venerable Mauser M98's are perfect with regard to the average parts changer who has little knowledge or experience. Barrels can require a little thread filing or even a quick turn on the lathe. Even more important though is headspace since Mauser barrels are not timed and will need to be adjusted for proper and safe headspace whenever they are changed out.

    You might consider a gunsmith in order to be assured of the safe functioning of your rifle.

    As an aside, I usually reserve the letters 'FNC' for the rifle developed for the 5.56mm cartridge:

    "The FNC (Fabrique Nationale Carabine) is a 5.56mm assault rifle developed by the Belgian arms manufacturer Fabrique Nationale (FN) of Herstal and introduced in the late 1970s."

    Best.
  • v35v35 Member Posts: 13,200
    edited November -1
    You can use machinists' blue or black marking pen on the barrel threads and run the barrel into the receiver.
    File carefully the spots where the blue rubs off. Repeat the bluing and work your way in. It's a slow but doable process.
    Keep threads of barrel and receiver clean of filing chips/dust.
    Grind a safe edge on the file to avoid cutting the face of the adjacent thread. You want a file included angle less than that of the sharp V thread. Leave some teeth at the bottom edge as you may need to deepen the thread in spots.
    All Mausers have sharp V threads and are of the same pitch.
    You may find thread o.d. or the root dia. needs touching up but only as much as determined by bluing wearing off.
    A test was performed on difference in accuracy between loosely matching and snugly fitted barrels both having same tightening torque.
    It was determined there was no difference.
    I've personally unbarreled twelve Springfield A4 sniper rifles that required a long pipe to break free. Following a loud screech, all spun out freely.
    There was a lot of filing and hand fitting going on in Germany necessitating S/N marking of parts.
    In the US there was and is a 100% fit and interchangeability of most parts.
    This has been going on here since at least the Civil war.
  • nononsensenononsense Member, Moderator Posts: 10,536 ******
    edited November -1
    slideways,

    "You can use machinists' blue or black marking pen on the barrel threads and run the barrel into the receiver.
    File carefully the spots where the blue rubs off. Repeat the bluing and work your way in. It's a slow but doable process.
    Keep threads of barrel and receiver clean of filing chips/dust.
    Grind a safe edge on the file to avoid cutting the face of the adjacent thread. You want a file included angle less than that of the sharp V thread. Leave some teeth at the bottom edge as you may need to deepen the thread in spots."

    This procedure is guaranteed to leave flat spots and poorly fitted threads. Thread filing should be done with the barrel in a lathe at the very least. Anything less is cobbling of the lowest level and will leave you with a poor fitted barrel. Besides, this thread profile is 55 degrees and not 60 degrees as with most common U.S. threads so unless your file is 55 degrees you're going to play havoc on this tenon.

    "All Mausers have sharp V threads and are of the same pitch."

    Not true. Siamese Mausers use a different thread pitch with 14 TPI.

    "A test was performed on difference in accuracy between loosely matching and snugly fitted barrels both having same tightening torque.

    It was determined there was no difference."

    A test? A single test? One event?

    If not a single event, how many elements and tests were conducted and under what circumstances?

    Loose is subjective. Your loose may be significantly different from mine There are far too many factors that come into play when trying to discuss fit.

    Besides the most important factor in accuracy is the straightness and concentricity of the hole down the middle of the barrel and the parallel/perpendicularity of the shoulder/inner ring contact.

    "There was a lot of filing and hand fitting going on in Germany necessitating S/N marking of parts."

    This statement is fallacious in general since the M98 pattern rifles have demonstrated extreme interchangeability since day one. This include almost every single M98 rifle from the beginning. The only part which has required fitting is the barrel and that usually stems from headspace as opposed to thread fit. This has been noted throughout the history of the Mauser.

    If the threads don't fit and you don't have any familiarity with lathe work, see a gunsmith and fore go the temptation to cobble something together.

    Best.
  • 260260 Member Posts: 1,134
    edited November -1
    like i said... check the threads with a pitch gauge against one another. quiet simple. 260
  • slidewaysslideways Member Posts: 9 ✭✭
    edited November -1
    Prussian blue shows full face contact and the barrel threads bottom in the receiver after the first thread. Original barrel's filed threads are .027" smaller (o.d.) than the Czech's good one's. Probably more interference than bright sun and cold water will fix. I can imagine some variation given numbers and manufacturer's over the years. Besides if it's that tight headspace, which will probably have to be adjusted, will be a real pia. I think making the threads smaller will probably lose to another barrel that fits better. Are Mauser's metric or SAE or both in threads? My Craftsman thread pitch gauge says 11 tpi on all. Yes indeed, the barrel is 14 tpi. on the Siamese Mauser, whose barrel threads in like I think it should. I assume timing the barrel refers to the extractor slot in it like the Siamese has? is that correct? The only reason I called it an FNC was because that's what is stamped in the receiver; thank you for the differentiation.
    Thank you
  • v35v35 Member Posts: 13,200
    edited November -1
    I hope you got my reply before it was deleted.
    A close examination of Lugers and other Axis arms by someone who recognizes toolmarks will reveal evidence of filing.
    Unlike U.S. small arms, many of their replacement parts needed adjustment by an armorer.
    Serial numbering of parts ensures handfitted parts are not installed in another soldiers' gun.
    Picking up a thread to make minute corrective cuts once the barrel has left the lathe setup isn't for the average gunsmith whose strength most likely isn't in the machine trades or he'd be in them.
    Careful bluing and filing may be the practical solution if your skills are up to it.
    All Mausers 71/84,1888,1889,1891,1894,1895,1896,1898 lg&sm ring also FN single shot Mauser actions have 12 pitch sharp V threads.
    Siamese Mausers may be an exception.
    Barrels removed from actions may likely have distorted threads
    that will need adjustment to fit another action.
  • nononsensenononsense Member, Moderator Posts: 10,536 ******
    edited November -1
    slideways,

    The Mauser M98 used the British Whitworth 55 degree thread form. The 12 TPI thread was the standard for all M98 rifles.

    We need to see pictures of the actions and barrel tenons to determine what the mystery is with the supposed 11 TPI threads that you report. Pictures should include the manufacturers name and any proof marks that could be used for identifying the actions and to help resolve the mystery.

    Best.


    v35,

    First and foremost:

    We are discussing the Mauser M98 RIFLES not Lugers or any other small arm. Paul Mauser designed and created the rifle and the machines which were capable of manufacturing parts that required little or no fitting and are completely interchangeable. Your obvious prejudice is handicapping the truth for this discussion. If you're not familiar with the history and details of the design and manufacturing, there is some fascinating reading which covers all of the details and will explain the processes.

    Second:

    Every gunsmith I know that works with rifles and barrels knows exactly how to pick up a thread in order to correct an existing error. This is not difficult at all, it is a common practice in every shop I've had the pleasure of seeing. In fact we teach it to every student who enters a gunsmithing program. You might be thinking of the wannabe cobblers who use Dychem and a file to attempt to correct a thread by hand.

    Best.

    Until we see some quality pictures, there is no reason to continue this.

    As an aside, what response did you post that got deleted? Do you have a copy of it?

    Best.
  • v35v35 Member Posts: 13,200
    edited November -1
    All this banter is academic, being the subject barrel is from a Siamese Mauser produced in Japan having a 12.7 TPI pitch.
    The barrel cannot be made to properly fit a 12 TPI Mauser.
    Sharp V 12TPI replacement barrels for Mauser actions have been successfully used for years.
  • nononsensenononsense Member, Moderator Posts: 10,536 ******
    edited November -1
    v35,

    The so-called 'banter' is definitely not academic when so much bad information gets expressed. It is proper on Ask the Experts to correct any misinformation so that the poster gets the best information available.

    How was it decided that this was a Siamese Mauser with a 12.7 pitch thread or is this just another guess?

    It's obvious that any thread other than the original 12 TPI is uncorrectable. Even amateurs should know this.

    Had this information been available from the start, much of this could have been avoided. But that's what comes from needing knowledge, it's hard to know where to start and what to tell.

    Best.
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