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Thread: M77 MKII misfiring

  1. #1

    Default M77 MKII misfiring

    I purchased a 300Wm from a close friend , and it fired one box of remington ammo , I was there when it fired those 20 rds , since I purchased it , it has missfired 14 times in 100 rds . I was thinking primers , but I loaded for several different rifles from that same batch of primers and havent had any misfire . I suspected the bolt was dirty internaly so I gave it a serious bath with brake clean and lubed it with remoil , same result 15 misfires outa 100 . Im leary of takin the bolt apart ,after watchin my smithy put the bolt back togather on my 358 NM . Has anyone had a cci primer problem or bolt problem like this , I have 3 other M77's and havent ever had a missfire.
    Thanks in advance

  2. #2
    Join Date
    Jan 2007

    Default misfires

    Ruger bolts are easy to take apart to clean. Just get a small punch to insert into the hole in the back of the firing pin. Now hold the bolt in your hand like a mic and place the bottom ledge of the firing pin sear engage area on a hard flat edge surface. Pull slightly down enough to insert the punch into the disassembly hole and release.
    the punch holds the pin back and now you just unscrew it out of the bolt.

    Before you do the cleaning try this 1st>> take the bolt and turn the back half to the left as you hold the bolt firing pin facing up. the cocking/sear surface should drop into the fired position. You can now measure firing pin protrusion at the bolt face. Write this down to check against factory specs and compare to the reading you get after cleaning and inspecting the firing pin. After measuring just hook the cocking/sear surface on the hard flat edge and pull and rotate back to cocked position and put punch in dissassembly hole then dissasemble as 1st instructions above.

    Use pipe cleaners to clean out the bolt body too. and dont oil the firing pin if you are shooting in freezing weather around zero or below some oils get gummy and thick at those temps and will rob about 1/2 or more of firing pin energy.The only oil i ever use is breakfree.


  3. #3

    Default Primers

    Some primers are HARDER than others. Try using a different brand of primers. CCI makes a Military primer for use in semi-auto rifles which are very hard. Try using a Federal Match primer they are very consistant and work very well, even on Remingtons with Titanium firing pins (used to decrease lock time). This should be done in conjuntion with a good bolt cleaning. Sometimes, small pieces of carbon, nylon and debrise can get trapped in a bolt. Also if you are shooting outdoors this time of yaer watch lubing the firing pin, as oils can freeze and cause problems.
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  4. #4


    how do the primers that misfired look? Is the pin straight? next tim it is out spin it and see. if you have protrusion in spec, the spring is at the right tension, and all is could be trigger mech issue or dirt, or contaminated primers

  5. #5
    Join Date
    Jan 2005

    Default Oops!!

    I am just now realyzing we have two identical threads here now. Thanks, Jedi. I don't know what to do with them since there are responses to both.

    I am not defending CCI or any primer maker. Nor am I defending a gun maker, if there is a problem with the Ruger, I'm sure they will fix it but of course the inconvenience of that does not a happy camper make.

    One test of the Ruger would be to take the bolt out and turn the cocking piece (back part of the bolt) and allow the striker to fall. This will push the firing pin out the firing pin hole in the face of the bolt. There should be about .030" protrusion of the tip of the firing pin. Compare to others if you have some.

    When reinstalling the bolt you will have to recock and that can be tricky. Hook the sear notch over the edge of the work bench and pull the body down and turn the cocking piece at the same time to recock. Also you can use the same batch of primers in a different rifle for a sample test.

    I would guess the rifle has a problem. But your smith may be able to get Ruger to send new parts, maybe.
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  6. #6
    Member Kurt S's Avatar
    Join Date
    Apr 2006



    Several years ago, I had a simular problem with a 7MM Ruger I've had since the early 70's. I would guess the missfires were about the same ratio you are seeing. I took it to a couple smiths here in town and got the same story, the fireing pin spring is getting weak. No one had one, and all were reluctant to even work on a "Ruger". Seems they had trouble dealing with Ruger on parts, or some such nonsense. This may be different now, but 10 yrs ago that's how it was.
    I boxed it up and sent it off to Ruger and got it back a few weeks later. They had replaced the firing pin and spring, checked it for function and sent it back. N/C. It hasn't misfired since so in my case, that was the problem. As to why some rounds lit off and some didn't, I can only guess it had to do with temperture affect on the spring at that point in it's life.

    Hope that helps.


  7. #7


    You say that u are reloading...make sure that you are not seating the primers too deep in the pocket. If you do you get no bang. just cuz the other guns worked isn't proof.


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