Need Some Help On This One......

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by dbhostler, Jun 13, 2003.

  1. dbhostler

    dbhostler Well-Known Member

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    Just purchased a Sendero SF in 7 RUM. While attempting to fireform some cases I ran into something I've never seen. The RP cases are severly dented just below the shoulder about 1/8th inch wide and 1/2 inch long and 1/8th inch deep. My thumb and nail fits very well into it. The cases also look as though they have been smoked by a candle. It's very apparent that the case is not sealing, but why? Is the chamber cut too long? Am I not using enough powder? FYI, I am loading 75 grains of RL-22 under a 180 grain JLK VLD with a 91/2M primer. I thought about casting the chamber, maybe this would show something amiss. Your input would be appreciated.
    db
     
  2. Warren Jensen

    Warren Jensen Well-Known Member

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    Can't be sure without measurements but what you are describing is the base of the bullet or the start of the boattail is clearing the case neck before the engraving seal is established. The gas pressure is blowing back and denting the shoulder before the case has completely explanded to seal the chamber. You probably are using long ogived, relatively shorter bearing surface bullets and have a very long throat. I saw this very thing in a factory chambered 7mm RUM Sendero. You can confirm by casting the chamber and/or using bullets with longer bearing surfaces.

    Warren Jensen
     

  3. dbhostler

    dbhostler Well-Known Member

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    Warren,
    I think the throat on this rifle is like the 300 WBY I once had, very long. That's why I seated the bullets into the lands to push the base against the bolt face. Would it do any good to attempt sizing the neck tighter to hold the bullet longer as well as loading a bullet with a greater bearing surface?
    db
     
  4. MachV

    MachV Well-Known Member

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    My Sweedish94 engineers carbine does the same thing with reloads and was wondering what caused this?The chamber & barrel are in ruff shape but it still shoots factory ammo good,no more Amaxes!
    Thanks for the info Warren.
    CJ
     
  5. Brent

    Brent Well-Known Member

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    The only time I've gotten sooted necks and bodys is when the cases needed annealed, other than that I can't see a problem with what you're doing. 10,000 psi is all it should take at most to expand the case and seal it up good. If it isn't doing that I'd anneal them. When they get hard and brittle they just won't open up and seal. Some of my Ultra brass seemed awefull hard to begin with to tell you the truth. I noticed this when my brother first got his too. The necks seemed a little thicker as well.

    If you use a hack saw or dremmel to cut off a short ring on a cases neck, chamfer and split this ring, seat a bullet into the short necked case now, slip this ring over the bullet and leave it out long. When you chamber this round the chamber will push the ring back when it hits the end of it, pull it out and measure the cases OAL now.

    This will tell you the trim to length, I trim to .005" shorter though. My 300 Ultra is exactly 2.840" to the end. Don't outside chamfer the end of the ring that hits the end of the chamber too much or it will stay out farther than it should.

    I've got dented cases just exactly as you describe too, just a little "below" the shoulder and running length wise about 3/8" long and 1/8" wide.... they all came from my damn FL sizing though. Didn't matter what amount of lube I use either. Something I've just lived with basically.

    How old is your brass?
     
  6. dbhostler

    dbhostler Well-Known Member

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    Brent,
    The brass is new, unfired Rem brass. The only thing I have done prior to fireing is to run the cases through a Sinclair expander die and chamfer the inside and outside of the neck.
    I also used a mag primer, maybe I should try a regular primer.
    db