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  1. #1
    Contributing Member gun papa's Avatar
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    Headspace question

    Do NM grade guns have tighter Chambers? I have a gun with a 1963 NM barrel. I have 1963 match rounds. When I disassemble the bolt and put a live match round in the chamber, the bolt lug will close all of the way with mild/ moderate thumb pressure. I have some standard 1942 ball where the bolt will almost close all of the way with moderate thumb pressure..

    I just got some Clymer headspace gauges. Will they read okay with my tight chamber?
    I really would like to shoot this thing. It's a beautiful gun. Just trying not to wreck it or me.

    See imgur albums
    Headspace/ bolt lug http://imgur.com/xxWV4m6

    The gun. http://imgur.com/a/7Iy41DI
    Last edited by gun papa; 03-22-2019 at 02:58 AM.

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    bob seijas's Avatar
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    NM Headspace

    Yes, they are tighter. After the first batch of NMs was evaluated by the Army rifle team in 1953, Bill Brophy wrote a scathing report on them and the simplistic way they were chosen. He was invited to attend the process at SA in 1954 and had a list of suggestions. Two of the recommendations were that candidates be selected for minimum bore dimensions and minimum headspace. These were adopted for 1955 and became standard thereafter.
    Real men measure once and cut.

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    Contributing Member gun papa's Avatar
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    Thread Starter
    Bob, how would I determine if it is safe to shoot? I just received my Clymer gauges, but I would assume they are for a standard 30-06 chamber. The stripped bolt closes on the match ammo like a dream, but I am apprehensive.

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    Sorry, not my expertise.
    Real men measure once and cut.

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    Contributing Member gun papa's Avatar
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    Quote Originally Posted by Bob Seijasicon View Post
    Sorry, not my expertise.
    Thank you.

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    Senior Member Wineman's Avatar
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    GP,

    Hatchers Notebook talks about how when a Garand cycles, the force will shorten the case (increasing headspace). It sounds like you have a minimum chamber. The danger would come from the bolt not closing all the way (with standard ammo hard to believe). The CMPicon recommends the use of Clymer gauges. If the bolt will close on the Clymer Go and not on the Clymer No-Go, they would pass the rifle. Maybe besides the Match ammo, you feed it a diet of factory "Garand" approved ammo, like sold by Hornaday, or Creedmoore. These will have cases that will fit a minimum chamber. My experience is that Factory ammo will fit the minimum dimension chambers. When firing, avoid rapid fire until you are sure the bolt is closing completely on every round. If you have ammo that does not chamber easily, if in doubt, stop. My M1903's detest any ammo that is not SAAMI minimum. So a case that is fired in my M1icon will not chamber in a M1903 without a F/L resize. Cases fired in the M1903 will chamber in the M1 (CMP Rack Grade) without resizing. With Clymer gauges the M1 passes the Go and not the No-Go.

    Dave

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    Contributing Member gun papa's Avatar
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    Quote Originally Posted by Wineman View Post
    GP,

    Hatchers Notebook talks about how when a Garand cycles, the force will shorten the case (increasing headspace). It sounds like you have a minimum chamber. The danger would come from the bolt not closing all the way (with standard ammo hard to believe). The CMPicon recommends the use of Clymer gauges. If the bolt will close on the Clymer Go and not on the Clymer No-Go, they would pass the rifle. Maybe besides the Match ammo, you feed it a diet of factory "Garand" approved ammo, like sold by Hornaday, or Creedmoore. These will have cases that will fit a minimum chamber. My experience is that Factory ammo will fit the minimum dimension chambers. When firing, avoid rapid fire until you are sure the bolt is closing completely on every round. If you have ammo that does not chamber easily, if in doubt, stop. My M1903's detest any ammo that is not SAAMI minimum. So a case that is fired in my M1icon will not chamber in a M1903 without a F/L resize. Cases fired in the M1903 will chamber in the M1 (CMP Rack Grade) without resizing. With Clymer gauges the M1 passes the Go and not the No-Go.

    Dave
    Thanks,Dave
    I got about 400+ match 1963 rds. My intension is a slow fire shooter for my twilight years. I figured I would reload and replicate the match loads dimensions. This is my first Garand and I just want to understand what I am doing and safely. I have had it since about June and I am in no hurry. I hope to strip her down today and try the Clymer gauges. I don't think there will be any problem locking on match or standard M1 ammo. Thanks for the help.

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    Senior Member MGMike's Avatar
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    The missing page in this story is whether your rifle has been rebarreled, and if so, whether the job was correctly done. New M1icon barrels generally are short-chambered with the expectation that they must be reamed when installed.

    If you have to use "moderate" thumb pressure (whatever that means as opposed to "light") to obtain full bolt rotation with a cartridge case made at or near the minimum tolerance, what will happen if you encounter ammunition in the upper tolerance range, or after the chamber accumulates some fouling? Answer: possibly incomplete locking that even the compression of the case from the bolt slamming shut under spring pressure may not overcome.

    A similar condition is sometimes seen with reloaded cartridges that have been incorrectly resized with the shoulder too far forward, resulting in insufficient headspace, even though the OAL might be fine. The consequence of that is "toenail" locking of the bolt allowing premature unlocking while chamber pressure is still too high. This can damage the receiver or bolt by shearing off the corners of the locking recesses or locking lugs.

    By all means test the minimum headspace with your "GO" gauge using only light finger pressure. Beware if you encounter any resistance. Moreover, it is cheap insurance to use a cartridge case gauge --available from Dillon's-- to make sure the cartridges you intend to use are within min-max tolerances.

    M

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    Really Senior Member Sunray's Avatar
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    What happens with a live round has nothing to do with head space. Only the gauges tell you anything. And head space is head space. The tightness of the chamber means the tolerance in closer. Not different.
    "...a case that is fired in my M1icon will not chamber in a M1903 without a F/L resize..." That's completely normal. Any time you use the same brass in 2 rifles, FL resizing is required. Of course, all semi-auto's require FL resizing every time.
    "...replicate the match loads dimensions..." Waste of your retirement time. Just FL resize, meticulously weigh every powder charge and use match grade bullets. Partial to 168 grain HPBT Hornady Match bullets with IMR4064 in my '03A4, myself. Mind you, an NM barrel does not mean the rifle will shoot like a NM rifle. Lots more to an NM than just the barrel. Bedding and such. There's a manual for that here. Note the need for the provided UN & PW.
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    Senior Member Wineman's Avatar
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    Good advice. I try to keep brass separate for each rifle. I did F/L size a batch of M1icon fired cases. For some reason a few did not get the shoulder pushed back. When I used them in a M1903A3 there were two that would not chamber. The shoulder was just far enough forward that they were not going to fit, no matter how hard I pushed on the bolt. Every other case was fine. Bad technique, springy brass, improper set up? Not sure. The two offending cases fit the M1 just fine, no thumb pressure whatsoever. The same rifle will not close on the No-Go Clymer, no way.



    Dave

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