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Thread: M1 Garand Expertise Needed - Double Firing

  1. #1
    Boolit Master mtnman31's Avatar
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    M1 Garand Expertise Needed - Double Firing

    My M1 Garand will occasionally double fire on me. Bam! Bam! with one pull of the trigger will certainly get your attention when you aren't expecting it. Any ideas of what is malfunctioning or what to look at?

    When the bolt goes into battery, could inertia be slamming the firing pin on the primer with enough force to ignite it? I didn't check while I was at the range to see if unfired cartridges (that had been chambered) were showing any indentations on the primer. I will definitely check that next time I take it to the range. I am using Federal primers which are "softer". If that isn't the issue, what else should I be looking at? Trigger assembly? Bolt/firing pin? All other function of the rifle is working perfectly.

    It is a CMP rifle that was converted to a National Match rifle back around 2002 by the Navy's Crane armorers (back when the Navy shooting team still had armorers).

    Any help would be greatly appreciated.

  2. #2
    Boolit Grand Master



    M-Tecs's Avatar
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    Doubling is common with both the M1 and M-14 triggers that have been stoned a little to much or heavily worn. The fix is simple and only requires a small piece of sand paper. The cause is your finger bump firing the trigger.

    http://www.biggerhammer.net/manuals/garand/trigger.htm

    One last thing to do, check the weight of pull again. For use in both NRA and National Board-sponsored service rifle matches, the trigger must hold a 4 1/2-lb. weight. That's also minimum safe weight of pull. If your trigger won't hold that weight, there is one more step to be performed.
    Take a 1" x 8" strip of 220-grit, Wet or Dry or emery cloth and insert it between the rear of the trigger and the attached disconnector, abrasive side against the trigger. This is done with the trigger housing group assembled, the hammer uncocked. Hammer spring tension in the assembly will hold the cloth in place. Making sure the abrasive surface touches only the trigger, slide the cloth back and forth using about half the length of the strip. Check the weight of pull about every fourth stroke until the trigger will hold the 4 1/2-lb. weight. Now you're done.


    http://www.milsurps.com/showthread.php?t=37213

    The second to the last picture on the milsurp link gives you a good visual

    If you don't want to do it yourself I will do it for you for free if you pay shipping both ways. I am leaving for out of state goose hunting and the holidays so I won't be back until the end of the month.
    Last edited by M-Tecs; 12-07-2019 at 07:11 PM.
    2nd Amendment of the U.S. Constitution. - "A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."

  3. #3
    Boolit Bub
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    That would certainly get my attention. Does it do it with factory ammo? I set my dies to move the shoulder back .004". To get that measurement I removed the gas plug, fired a round in a fouled chamber, extracted it and used a RCBS precision mike to measure the case while adjusting the sizer die. I also use CCI 34 primers although I used Winchester LR primers in the past with no ill affects.

  4. #4
    Boolit Bub
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    you may be milking the trigger, hold the gun solidly, do not let it bounce in your hand you may be double taping and not know it.

  5. #5
    Boolit Master Hick's Avatar
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    all the above-- but also, the firing pin channel in the bolt may be gunked up a little. If the firing pin stays out a little after the first shot the second round may slam fire. That second firing will probably push the firing pin back enough so that the next round is OK.
    Hick: Iron sights!

  6. #6
    Boolit Master
    lefty o's Avatar
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    as cub45 mentioned, off the bench, milking the trigger is the usual cause for this with people new to the rifle. pull the trigger with a purpose.

  7. #7
    Boolit Grand Master

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    M Tecs fix is what probably needs done. A tuned trigger in the garand will slowly smooth and drop weight in use. When I did a trigger I set it up at 4 43/4 lbs to 5lbs. This would drop in and stay longer. Another point when working the trigger you can get close outside of the rifle but the final needs the stress of locking the rifle receiver down to get it just right. Look at the trigger hooks as rounded edges can also cause this. Weigh the trigger and see where it is at. Another trick with the garands and similar is to pull the trigger and hold back till functioning is completed. Im betting bolt slam is bouncing the hammer hooks off the trigger occasionally.

  8. #8
    Boolit Master
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    It could also be the Federal primers. The only time my M1 slam fired on me was with federal 210's I gave the charging handle a hard shove to chamber the first round and BANG. I should have known better than giving it that hard of a rap. I have seen M1a's slam when the shooter put a round in the chamber pulled back the handle an let'er go without a magazine in place to slow down the bolt momentum he was using federal 210m match primers. I'm not knocking the federals I use 210's in everything that takes a large rifle primer and this is the only bad experience Iv'e ever had with them,heck the last time I got primers I lucked into 4 cases of 210's with the same lot number.
    Last edited by 1Hawkeye; 12-08-2019 at 12:04 AM. Reason: more data

  9. #9
    Boolit Master rmcc's Avatar
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    +1 on HICK's post.....IMO, most doubling problems with an M1 are firing pin related UNLESS trigger/hammer have been stoned too much.
    fools rush in where angels fear to tread...Alexander Pope

  10. #10
    Boolit Master
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    Second vote to check the primers. the M1 has an inertial firing pin and will put a slight dimple on any round. That is why mil spec primers have a harder cup.
    jim

  11. #11
    Boolit Master
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    Remove bolt and disassemble and inspect for kinked springs and a chipped extractor face, firing pin condition. Assemble and check protrusion/retraction, flush rear and .044"-.060" protrusion just for general inspection. Then my money is on really worked piece that was on the ragged edge that has shot itself out of sweet, a new trigger assy fitting would be my educated guess. I had a few over the years being so sweet and crisp when done in hand, and double tap at range. Trigger control of not letting off or not pulling through and magic spot held to bounce disconnector, the double tap startles you and you let off and it stops.

  12. #12
    Boolit Grand Master



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    Last edited by M-Tecs; 12-08-2019 at 03:36 PM.
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  13. #13
    Boolit Grand Master

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    The garand and M1-A M14 have a slot in the receiver bridge that catches the firing pins tang and restricts for ward movement until the bolt is locked. Its not fool proof though. ( nothing mechanical is). One important thing when a double occurs is if possible look in the receiver and see if the hammer is down or still cocked, This gives an idea of where the problem is. trigger or slam fire.

    A lot of the military teams guns were built on the edge for best performance. But they also had armorers on the range to fix problems. I still remember the Army and Marines semi trailers behind commercial row where the armorers worked and did repairs. For awhile they did the trigger weighing also. A lot of there 600 yd loads were upper end also. For quite a few years you could drop your civilian rifle off and have it fixed up graded for cost of parts and a few beers LOL.

  14. #14
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    Quote Originally Posted by country gent View Post
    One important thing when a double occurs is if possible look in the receiver and see if the hammer is down or still cocked, This gives an idea of where the problem is. trigger or slam fire..
    Except if the gun fires the second time, the bolt cycles and the hammer gets cocked again and stays cocked unless the disconnector/sear doesn't catch it,,, in which case it goes full auto.

    This problem sounds like soft Primers to me.

    Randy
    "It's not how well you do what you know how to do,,,It's how well you do what you DON'T know how to do!"
    www.buchananprecisionmachine.com

  15. #15
    Boolit Grand Master



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    I've done maybe 200 or 250 trigger jobs on M1's or M-14's. Everyone one that has doubling issues was corrected by process laid out in post two.

    I have only shot a limited number of Federal primers in an M1. I have fired a large number of Federal Gold Medal Match in M-14's without issue. Same for a lot of the Highpower Service Rifle competitors.

    I have witnessed two out of battery slamfires in M-14's or M1A's. One was due to a broken firing pin and the other was suspected high primer. The shooter had several high primers in the remain loads. In both cases the cartridge case blew the head and their was significant damage to the guns.

    With service weight triggers I can get most M1's or M-14s to double from the bench if I milk the trigger.

    For those that want to test if they can get a Federal primer to slamfire in an M1 or M-14 it's simple and safe to test. Take a primed sized case and chamber it. In an M-14 don't insert the mag and let the bolt slam closed. If you doesn't slamfire under the most extreme case it won't when the bolt is stripping a cartridge from the mag and yes I have tested this in M-14. Never tested it in an M1 but the same test can be done.

    Also the M1 and M-14's have free floating firing pin but it is not an inertial firing pin.
    Last edited by M-Tecs; 12-09-2019 at 11:01 AM.
    2nd Amendment of the U.S. Constitution. - "A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."

  16. #16
    Boolit Master mtnman31's Avatar
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    My trigger weighs in at exactly 5lbs. I'm definitely not milking the trigger. My prone position (when slung up) is pretty rock-solid, so I don't think it is any of "my mechanics". I can't find anything overtly wrong with the bolt/firing pin. The pin moves freely, everything is smooth, no burs, etc. I've got another Garand that I can swap trigger groups with and see if the problem follows.

    I'll hit the range this week and double check on the primers of some unfired rounds and see if inertia is leaving some substantial indentations on the primers and possibly slam firing. I think I may still have a few rounds of GI surplus ammo that I can also try and see if it does it with that.

    Thanks for all the replies. As always, the gang here is helpful and the posts educational.

  17. #17
    Boolit Master


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    To (hopefully?) add something else to look at: You are using reloads; if the brass is U S military, the original primers were swaged in. All sorts of gizmos abound to make the primer pocket SAAMI spec'd. (I use the Dillon tool).
    Two suggestions, if this be the case: 1st: Use a tool to get primer pockets to appropriate size -- diameter and depth. Diameters run from 0.2085" to 0.2100". Primer pocket depths run from 0.1230" to 0,1360". And, 2nd, make sure NO primers are even a smidgeon higher than the case head. I used to simply run a metal 6" ruler straight edge across; others, just check with a fingernail. I have a tool my Dad had made for this purpose, using a dial indicator.
    Also, I very strongly suggest NOT using Federal primers due to their softness; and, I know I ONLY use CCI #41 primers in my '.06 Garand loading.
    CCI has a blurb on their primer page re these, and pasted here:

    "Military-style semi-auto rifles seldom have firing pin retraction springs. If care is not used in assembling ammunition, a “slam-fire” can occur before the bolt locks. The military arsenals accomplish this using different techniques and components—including different primer sensitivity specifications—from their commercial counterparts. CCI makes rifle primers for commercial sale that matches military sensitivity specs that reduce the chance of a slam-fire when other factors go out of control*. If you’re reloading for a military semi-auto, look to CCI Military primers.
    *Effective slam-fire prevention requires more than special primers. Headspace, chamber condition, firing pin shape and protrusion, bolt velocity, cartridge case condition, and other factors can affect slam-fire potential."
    BEST!
    geo

  18. #18
    Boolit Grand Master



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    When I first started shooting NRA Highpower Service Rifle Competition with M1's and M-14's I only used GI ammo or loads with CCI #41 primers. After watching the military teams shoot 100,000's of Federal Gold Medal match I became much less concerned. The only doubling issues were trigger or trigger control related. It's easy to tell the difference. When you have a double inspect the primers. If one has a normal indent and one is shallow you had slamfire. If both normal you had a trigger or trigger control issue. A full depth primer indent only happens when the firing pin is hit by the hammer. The M1 an M-14 firing pins are free floating but they are not inertia type firing pins. With inertia pins when the hammer is against the back of bolt the firing pin is shorter than the firing pin channel.
    Last edited by M-Tecs; 12-09-2019 at 12:18 PM.
    2nd Amendment of the U.S. Constitution. - "A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."

  19. #19
    Boolit Mold
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    If it's just doubling occasionally, you're most likely just bump firing it. Pull it tight to you shoulder and pin the trigger to the rear after the shot breaks.

    If it doubles all the time, or has a single-stage break, then look into the corrections that M-Tecs posted.

    Also, having a pull weight of <4.5lbs on the M1/M14 trigger is unsafe. If yours measures below this, then it must be addressed before continuing to use the rifle.

  20. #20
    Boolit Man
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    My M1 will double when using Federal 210 M primers. I switched to Win. WLR, reworked the loads, and have had no trouble since.

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