case mouth chamfer and runout

SPAK

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Apr 3, 2009
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how do you guys chamfer your case mouth? I was thinking about getting the one that fits in the wilson trimmer. Trying to reduce runout and wasn't sure if just using the hand held chamfer tool might be contributing to my runout...

I don't have a concentricity gage yet, it's coming in the mail, but when I roll the rounds on a mirror I can see the tip of the bullet wobbling pretty noticeably.

using redding body die
lee collet neck die
redding comp seater.
wilson trimmer

any thoughts?
 

mdmp5

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  • May 7, 2009
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    Re: case mouth chamfer and runout

    Not sure is chamfering is a strong solution to runout. It just lessens the scratching of the bullet by the case for the most part. But maybe there is an argument that it provides for easier seating. In any case, I chamfer my cases lightly before every loading with a forster chamfer/debur tool chucked in a sinclair holder.
     

    SPAK

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    Re: case mouth chamfer and runout

    I guess I'll know more when I get my concentricity gage but, I would assume that if I can visually see the wobble rolling accross the mirror, run out can't be good.

    I read somewhere that an uneven chamfer can contribute to runout but how much?
     

    mdmp5

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  • May 7, 2009
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    Re: case mouth chamfer and runout

    ANything is possible, but runout usually is the product of poor components and seating die, but you are using the comp seater so that shouldn't be an issue.
     

    SPAK

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    Re: case mouth chamfer and runout

    brass is lapua, neck turned, shell holder is clean and retaining clips is replaced with an rubber oring...
     

    madd0c

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    Re: case mouth chamfer and runout

    I have a wilson VLD chamfer tool that goes in the wilson case trimmer. I get about the same runout with it that I get with a vld on a rcbs trimmate and hand holding the brass. One thing I have definitely noticed is that if you don't neck turn, the wilson tool shows you the neck variations with an uneven chamfer.

    The wilson tool is very good, it is almost to good. I way over chamfered the first few cases I did and ended up with microthin case mouths that would deform just putting thumbnail pressure on them. If you go with the Wilson, it only takes about 5 turns with light pressure to get a good chamfer.

    madd0c
     

    SPAK

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    Re: case mouth chamfer and runout

    thanks, I have a wilson with the vld chamfer for the trimmer coming in the mail. I figure I might as well get as even a chamfer as I can if I'm going through all the trouble to reduce run out.

    any other thoughts on where I might be getting run out enough to visibly see wobble?
     

    Fuzzball

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    Jan 19, 2009
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    Re: case mouth chamfer and runout

    An uneven case mouth would have to be massive to cause visible runout.

    Most run out is from poor necks. Nonconcentric or uneven thickness OR a poor sizer/expander making the necks crooked. No seater can correct a poor bent or uneven neck!

    Perhaps the biggest cause of "bent" necks is a conventional ball expander that drifts to one side, due to neck variations, as it's withdrawn. I use a Lee universal decapper followed with Lyman M dies for expanding FL cases and use Lee Collet Neck Sisers for neck sized cases. I do have one body die and use the Lee die in combonation with it for "FL" sizeing for one very accurate rifle; love the effects of that combo.

    From what I read on the net it seems many people think a high "bullet tension", a neck that's 3-4 thou under bullet diameter, is good. It is not. Such a hard forced fit into the case almost certainly produces signigicant run-out during seating. Seems the ideal "tension" is 1 to 1.5 thou.

    A really good seater die (and that means a Forster BR or Redding Comp seater) will keep things straight but only if the necks are good.

    One popular idea is to seat a bit, stop and rotate the caee and seat a bit more, etc, to reduce runout but that's virturally useless. Conventional seaters simpy aren't fitted tightly enough for rotating during seating to accomplish anythimg. If a bullet starts entry tilted it will usually continue that way. A proper neck tension helps them enter straight and the Lee or Lyman M dies assure that for me.
     

    Fuzzball

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    Jan 19, 2009
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    Re: case mouth chamfer and runout

    An uneven case mouth would have to be massive to cause visible runout.

    Most run out comes from poor necks - nonconcentric or uneven thickness - OR a poor sizer/expander making the necks crooked. No seater can correct a poor neck!

    Perhaps the biggest culprit to "bent" necks is a conventional expander that slides to one side due to neck variations as it's withdrawn. I use Lyman M dies for expanding FL cases, use Lee Collet Neck Siser for neck sized cases. I have one body die and use the Lee die in combonation with it for "FL" sizeing in one rifle and love the effects of that combo.

    From what I read on the net it seems many people think a high "bullet tension", a neck that's 3-4 thou under bullet diameter, is good. It is not. Such a hard force fit into the case almost certainly produced signigicant run-out during seating.

    A good seater die (that means a Forster BR or Redding Comp seater) will keep things straight but only if the necks are good.

    Popular idea is to seat a bit, stop and rotate the caee and seat a bit more, etc, to reduce runout is virturally useless. If a bullet starts entry tilted it will usually continue that way. Conventional seaters simpy aren't fitted tightly enough for rotating during seating to accomplish anythimg.
     

    Fuzzball

    Gunny Sergeant
    Full Member
    Minuteman
    Jan 19, 2009
    2,165
    5
    Re: case mouth chamfer and runout

    An uneven mouth chamfer would have to be massive to cause visible runout.

    Most run out comes from poor necks - nonconcentric or uneven thickness - OR a poor sizer/expander making the necks crooked. No seater can correct a poor neck!

    Perhaps the biggest culprit to "bent" necks is a conventional expander that slides to one side due to neck variations as it's withdrawn. I use Lyman M dies for expanding FL cases, use Lee Collet Neck Siser for neck sized cases. I have one body die and use the Lee die in combonation with it for "FL" sizeing in one rifle and love the effects of that combo.

    From what I read on the net it seems many people think a high "bullet tension", a neck that's 3-4 thou under bullet diameter, is good. It is not. Such a hard force fit into the case almost certainly produced signigicant run-out during seating.

    A good seater die (that means a Forster BR or Redding Comp seater) will keep things straight but only if the necks are good.

    Popular idea is to seat a bit, stop and rotate the caee and seat a bit more, etc, to reduce runout is virturally useless. If a bullet starts entry tilted it will usually continue that way. Conventional seaters simpy aren't fitted tightly enough for rotating during seating to accomplish anythimg.
     

    madd0c

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    Mar 6, 2010
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    Re: case mouth chamfer and runout

    Holy triple post Batman!

    Fuzz, did your mouse stutter?

    However, despite the triple post, I agree with all that you said except the 3-4 thou under bullet diameter.

    I typically use SEATED NECK DIAMETER - .002 for my S type bushing dies to get consistent neck tension.
    This ends up being .008 to .01 OVER bullet size to get the proper tension depending on brass thickness.

    madd0c