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Thread: Tight closing bolt help needed on factory PPU ammo please

  1. #1

    Tight closing bolt help needed on factory PPU ammo please

    Hi chaps,
    I have a ZKK601 .308 that I have always used PPU 165gr rounds in as they were the 1st ones I tried when I bought the rifle and they group great. Whilst at the H4H shoot, I ran out so had to buy some at Bisley, but they only had some GGG 168gr which I bought and used (very well I might add get 40/50 on the running deer!!)

    What I noticed was how much easier the bolt closed using the GGG ammo as opposed to the PPU.

    What causes the tightness when closing the bolt with certain factory ammo?
    Is it safe to use ammo where the bolt is tight to close?
    Will it affect acuracy? This may (hopefully) be the reason I shot like a muppet on the stalkers test!!
    Is there anything I can do to check for problems, ie, colouring in a round with black pen and looking for marks, etc? I have a couple PPU left in the ammo safe at home so don't need to buy a full box to try.

    I know the chamber is nice and clean but I've never had the bolt to bits to clean so maybe this could be an issue? If so anyone know how to dismantle a ZKK601 bolt for cleaning?

    Cheers

    Stratts
    Follow my stalking journey & SD sponsored DSC1 progress blog here

    DSC1 forum sponsorship - Blogs - The Stalking Directory

  2. #2
    When I tried PPU in my Tikka 243 both the 90 and 100 grain were really tough to close the bolt. Shot ok but not great, the two weights of PPU in my 308 shoot terribly but the bolt closes fine. I've read on here before that quite a few people have the same tight bolt with PPU ammo.

  3. #3
    I have a ZKK601 in .243 as well but have not used it for ages. I'll check how it compares later as I honestly can't remember if it is as tight or not!!
    Follow my stalking journey & SD sponsored DSC1 progress blog here

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  4. #4
    Now that I've started reloading I plan to FL size some of the PPU brass and see if it fits any better or not.

  5. #5
    Stratts

    Two small questions:

    Do you clean the bolt lug recess? Could be full of gunk.
    Do you lightly lube the rearwards face of the bolt lugs? No lube is not good, too much lube is not good either.

    Regards

    JCS

  6. #6
    As far a I know the brass is thick on the PPU and causes it to be tight to chamber.

  7. #7
    Hi mate

    Yes to cleaning the lug recess of sorts! I have never applied any cleaning product (I use wipeout) but I do use a cleaning mop on a short rod to wipe around in there. Maybe it needs a good soak and scrub out?!

    No to lubing the bolt lugs! I do think the bolt needs a good clean (hence one of the questions) but I'm not sure how best to do it and if it comes apart easily? It looks like the end unscrews by using a big screwdriver but I'm not sure,

    Cheers

    Stratts

    Quote Originally Posted by jcampbellsmith View Post
    Stratts

    Two small questions:

    Do you clean the bolt lug recess? Could be full of gunk.
    Do you lightly lube the rearwards face of the bolt lugs? No lube is not good, too much lube is not good either.

    Regards

    JCS
    Follow my stalking journey & SD sponsored DSC1 progress blog here

    DSC1 forum sponsorship - Blogs - The Stalking Directory

  8. #8
    Quote Originally Posted by in2stella View Post
    As far a I know the brass is thick on the PPU and causes it to be tight to chamber.
    It's not a brass thickness issue, instead most likely a spec / tolerances one. Rimless cartridges such as the 308 Win 'headspace on the shoulder' that is the chamber and case dimensions from the locked & cocked bolt-face to a line around half way up the chamber shoulder section called the 'datum line'. The cartridge / case is similarly specified from the case-head to a matching invisible [datum] line on the case shoulder.

    The cartridge controlling and registration body, in this case the American SAAMI for the 308W, produce the toleranced drawings for both to be used by all manufacturers. As nearly all affordable mass manufacture has to allow some tolerances from the ideal, the max and min allowed tolerances are quoted. For all ammunition to fit into all rifles, the cartridge case max allowed value for this measurement has to be a fractionally shorter value than the same aspect of the rifle chamber at minimum tolerance level.

    In practice, most factory cases trend towards minimum and most factory rifle chambers towards maximum giving easy chambering of a new case / round but at the expense of a larger gap (excess headspace) than may be ideal for case life / accuracy. (Most people who handload set their full-length sizer dies too far in the press frame and also produce this situation or worse.)

    Occasionally, you get a minimum SAAMI chamber and slightly over-max headspace case giving a slightly tight case to chamber fit. Not ideal, but there is no safety risk as long as the bolt can be fully locked. Fired brass retains that form and if it is neck-sized in a reload will continue to be hard to chamber, more so in fact as shoulders migrate forward slightly under firing pressures even if a crush-fit before firing, so a FL or 'shoulder bump' body die has to be used to 'bump' the shoulder back a few thou'.

    A tight fit situation as described should show 'witness marks' on the case-head from the bolt being held hard against the face and turned in bolt lock-up and (possibly) smaller less obvious marks on the case-shoulder from being forced against the matching chamber surface on lock-up.

  9. #9
    Thanks mate I'll take a good look at the spent cases I have from both the PPU and GGG for comparison,

    Stratts
    Follow my stalking journey & SD sponsored DSC1 progress blog here

    DSC1 forum sponsorship - Blogs - The Stalking Directory

  10. #10
    I definitely had bright smears of brass on the case head after unchambering.

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