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Thread: Case head marks - help

  1. #1

    Case head marks - help

    I have been noticing some radial marks, scratches, on the heads of my cases. I can't say for sure if these are happening in the reloading dies, or the priming tool or in the actual rifle when shooting and so need to do lots more research but I thought to ask here just in case anyone has seen this before. The rifle is a Blaser R93 so it is straight pull but even so I have a feeling that it might turn the case slightly on extraction, though not my enough to leave these marks I suspect. The background is that this is a 308 and I've been working up a load for about 2 - 3 years now, I'm in no rush and new to this so it is all an adventure. I suspect that the marks have appeared fairly recently but am confident I am seeing them on cases with very moderate loads as well as on cases with my "deer" load. All loads are within printed book max for what that is worth. Here are a few photos:




  2. #2
    How about buying a box of factory "unmarked" ammo & firing them off. If no marks then you can at least eliminate the rifle as the cause.

  3. #3
    Any foreign bodies on the bolt face?
    (The Unspeakable In Pursuit Of The Uneatable.) " If I can help, I will help!." Former S.A.C.S. member!

  4. #4
    I haven't noticed this with factory ammo, but then I don't shoot much factory ammo now that I reload.

    I also haven't noticed any foreign bodies on the bolt face, or on my dies for that matter either.

    It is a bit odd as the marks look, to me, like they have quite clearly been made by some hard foreign object which has cut into the case as either the case or the object are rotated. There is no sign of smearing of the lettering, for example, which would be a clear pressure sign and I'm not seeing any other pressure signs. I do have some new Lapua cases here which I could do testing with but I thought to ask just in case someone out there with more experience than I would step up with "I know what that is, you need to back off..."

    One reason why I'm interested in opinions is that I managed to shoot my current "deer" load over the chrony this morning and the results were interesting, my previous load turned out to be giving me marginal deer legal velocity so I've worked up a little.

  5. #5
    Caorach, that mark you have on your cases is a "witness mark", engineer speak for two or more metallic faces that have contact, either together or with something extra being introduced between the faces, you will have an opposite surface or feature that will be making these marks, as they appear to be rotational, that would suggest the bolt face is making them, even a very small projection can be the cause, have a real good look under some magnification...... if it's a box mag, also check the ends of the lips on the box.
    (The Unspeakable In Pursuit Of The Uneatable.) " If I can help, I will help!." Former S.A.C.S. member!

  6. #6
    I hope you are right finnbear, though your answer is what i was wanting to hear. My concern was that it was, in some way, in indication of pressure but as you say it looks like a witness mark of some description. That being the case my best bet is that it came from one of the shell holders rather than the bolt as factory ammo is all ok plus my Blaser is a straight pull and so may not rotate the case much on extraction.

  7. #7
    Caorach,
    You say you have some new Lapua brass? why don't you put them through the press, & check them, then you'll notice any marks. If none then look for the foriegn body on the bolt face. But to be sure try some factory fodder as-well.

    Atb,

    Moe..
    Don't put your fingers, where you wouldn't put yer " Pecker"

  8. #8
    Distinguished Member Ronin's Avatar
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    I also have a Blaser.

    The bolt head is captive and cannot rotate.

    Therefore I do not think that the marks are caused by rotation of the bolt head on the case.

    Likely is a burr on the mag lips or foreign body on the bolt head itself.

    It is also possible that there is something in the case holder of your press which has created the witness mark when you FL size the case.


    I think you will find something on any of the three possibilities mentioned that has caused this.


    I dont know if you bought these cases new or aquired them from a third person ? - there is also a possibility that the marks were there when they came into your hands.....


    Try new brass after cleaning, bolt head, checking mag and cleaning case holder.

  9. #9
    Quote Originally Posted by Redmist View Post
    I also have a Blaser.

    The bolt head is captive and cannot rotate.

    I dont know if you bought these cases new or aquired them from a third person ? - there is also a possibility that the marks were there when they came into your hands.....
    Thanks for this Redmist, I was sure I had read that even the Blaser rotates the head slightly to get extraction, but I could well be wrong on this as like you say I can't see how it can possibly do it.

    The cases were new so I'm causing the scratches somehow. What it will need is me to get a new case and introduce it into the system and monitor its condition at each stage until it gets marked. I have a sort of feeling, which I can't support, that it is happening with the shell holder in my Lee hand priming tool. As you can imagine my main concern is that it isn't some obscure indicator of pressure. The cases have been reloaded, using this load, several times now and primer pockets are still tight plus as can be seen from the images there are no clear pressure signs. However on Saturday I shot one over the chrony and the velocity was, to put it mildly, remarkable. That caused me to step back and examine things again and these scratches were the only strange things I could find that were unusual, however I'm pretty sure they came into being with much milder loads.

  10. #10
    Distinguished Member Ronin's Avatar
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    The bolt head and collets on the Blaser are held in the bolt body by a sliding key, which locates in a groove within the rear of the bolt head assembly - when located and locked into the bolt head there is 2-3 degree's of rotation (nominal) when fixed.

    The collets do not rotate when the bolt is cycled, neither does the bolt face - extraction is carried out by the extractor and plunger working as the bolt is drawn rearwards.


    The case doesnt rotate during this phase or the firing phase.


    Interesting point regarding the Lee primer - it may be this, but the grooves are pretty deep - you'd have to give the cases a shove in a tight fitting case holder (with a burr) to create the mark.


    Can happen, I guess.


    Be interesting to see what the eventual cause is.


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