Timing of receiver and barrel
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  1. #1
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    Default Timing of receiver and barrel

    On another forum there has been ongoing discussion over the years about the interchange ability of US Krag barrels. It seems that you can unscrew the barrel on one Krag and put it on another with the sights, extractor cut and index mark all lining up. Also head space works out with little or no issues. We are not sure when this interchange ability started but the last change to the barrel design came on the 1898s at serial number 213,000. It is possible that earlier barrels will interchange on later receivers and line up by just adding a radius to the corner of the barrel.
    amach_-_barrel_threads.jpg
    Serial numbers on Krags go up to about 470,000 that is a lot of rifles with interchangeable barrels.
    Question- do any present day gun makers do this? Any other notables in the past that timed the barrels for easy interchange?
    That other forum is Krag Collectors Association.

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    Springfield o3/a3’s do this as do garands and m14’s
    I don’t think modern manufacturers do it in bolt rifles as none are sold with front sights anymore and if they are they are installed after barrel installation.

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    I can tell you that for a military rifle like an m14, the individual parts weren't built to such tight tolerances that you can assemble up a GI bolt, barrel and receiver and know what the end result is going to be. Some manufacturers tended to be more at one end of the allowable tolerances than others. If you want something up to match quality, you start with a short chambered barrel and hand finish it the exact headspacing you want. Otherwise, you might only pass the test of it not closing on a field gauge, which is acceptable for their original intent, but nothing we would strive for.

    I wonder what the head spacing might be on a Krag assembled in such a manner?

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    Quote Originally Posted by Grizzlypeg View Post
    I wonder what the head spacing might be on a Krag assembled in such a manner?
    Saami for the Krag is .064 to .071 max, no mention of a field gauge. I guess it was an advantage to have all the Krags built at one facility. The gauges they used to check timing would have had to wear over the course of almost a half million built.

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    Hi:
    "Timing" is a poor term on a Krag. You are doing two things, getting the front sight perpendicular and getting the extractor cut in the proper location.

    Almost all of the rifles mentioned were made on manual machines as fast as possible for war time production. The last Krag was made around 1900. Their idea and today's ideas of tolerance are pretty different. What most of these experts forget, is all of the rifles mentioned were final head spaced by swapping bolts out. Chambers and bolts were made with lots of variance due to the speed for war production and tools available. The guy barreling or re-barreling had a bucket of bolts and swapped them in barreled actions until the gauges said O K. English Enfields had removable bolt heads that came in different lengths - 1 to 5 to head space.

    I have shot a lot of Krags, Springfields and M1's (worn out many barrels). I have changed several barrels. They usually have a witness mark on the action and arsenal barrels. You screw in until the marks line up. Some screw in easily and some don't! Sometimes you have to cut the barrel face where it meets the action face to screw it in enough and sometimes you end up lapping the threads in to get them to fit up. Most of the time the head space is off. If the chamber is short, just sink in the chamber with a reamer. If too long you have to cut the chamber face on the barrel and sometimes the cut the chamber end of the barrel (cone). Re-chamber to Sammi specs. Do not shoot a military rifle that has had barrels swamped with out testing with head space gauges. I have had the pleasure of having an M1 fire out of battery (twice). It gets very exciting and loud! Digging the brass out of your face is less fun.

    Kreiger barrels has a subsidiary company called Criterion Barrels. Criterion makes very high quality button rifled barrels contoured, threaded and parkerized for a Krag for about 225 bucks (also M1 and Springfield). They also have the sight cuts and extractor cuts in the barrel. They are short chambered so you line up the extractor cut & front sight, unscrew and final chamber. If you are using a scope, cut off the first inch or so and line up the extractor slot. Barrel Link: Civilian Marksmanship Program eStore

    I wish the Krag guys lots of happiness and luck swapping barrels. Remember most of them do not understand fits, tolerances and how small a couple of thousands is.
    Well I guess someone put a bunch of quarters in my "on button" slot. For better or worse, that is my 2 cents worth.
    George

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    All the guys that did the arsenal rebuilds are dead now so we can not ask them. Of the many Krags sold to civilian some were brand new and others may have been rebuilt once or twice. During rebuilds parts were pulled from bins and many rifles and carbines will have this year receiver with that style bolt and another year sights. On the Krag I just built I found a case that was .001 below max and turned a step on the end of the barrel so I had .002 play in the bolt to give a calculated .065 head space. The receiver and bolt were both worn so that the guide rib on mine actually contacts the receiver. Even with that amount of wear the barrel step was only .005 to make it relatively tight.
    As far as I know bolts really only vary very worn and to no wear. I know of know marks to indicate large and small.
    Because of wear I think your advice on checking headspace on a swap is wise. On my take off barrel you can see the wear from the rim on the end of the barrel, another source variation. These things are over 100 years old! I will ask the supplier that has thousands of new Krag bolts if there are any marks to indicate head space incremental variations.

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    Springfield Armory worked to zero tolerance prior to WWI.The parts were perfect or scrap.There is a book by Fred Colvin called Manufacture of the Springfield Rifle that discusses this.The threads on M1 and M14 rifles and M1 carbines were timed.This was done with a thread milling machine.I suspect 03 and M17 barrel threads were timed as well.

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    QT : [The gauges they used to check timing would have had to wear over the course of almost a half million built.]

    Gauges would be inspected and if the limit was 50 millionths and off limit, then the gauge would be replaced.. IMHO.

    We had crazy tight limit gauges in the big shop.

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    As an example I said," English Enfields had removable bolt heads that came in different lengths - 1 to 5 to head space." not Krags.

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    03 threads were milled in the receiver, and timed (clocked?).

    The barrels were threaded, and maybe chambered, and then a gauge was threaded on that had a punch for the index mark.

    The index mark was used to index the barrel in a fixture for milling the extractor and sight features.

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    If I screw a Lithgow 1960 made SMLE 303 barrel into a Martini Henry action made in 1873,the barrel indexes correctly,with the flat face on top,and the sights correctly aligned......Once a machining operation was established,it was obviously followed right to the end .

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    I have since talked to the fellow selling new Krag bolts, said he has sold thousands with no complaints. That is not definite proof as Krags with the rimmed case are very tolerant of loose head space. But if any of the bolts had been tight and did not chamber factory ammo I am sure he would have heard something. Another Krag devotee that has swapped barrels and bolts extensively and checked his results with commercial go and no/go headspace gauges said he only had one bad bolt that did not head space right with other combinations of receivers and barrels. We think that bolt was worn or subjected to an overload that set it back.

    I had originally thought that Ford had pioneered interchangeable parts and the production line, but it looks like the old arsenals were ahead of him.

    I was trying to edit one of the old post and it timed out while editing.
    I know of no know marks to indicate large and small.
    That was one intended correction. GeorgeM, we are still trying to figure out if there are any marks that would indicate headspace variations on the Krag but so far none.

    If KenT is correct all that were not correct were scrapped, were the holes in the serial number sequence filled with replacements? We have had a discussion over at KCA whether the serial numbers were done before or after heat treatment. If before there would have been hole in the sequence that could have been replaced or not. I have never stamped a case hardened receiver, but it seems to me the proof stamps and others done after hardening would not last very long.

    Back to bolts, I am thinking about how to gauge them and looking for a variation from the mean and if any of the stamped marks correspond. attached photo is a quick and dirty representation of how I would check.
    kragboltrs.jpg


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