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Crimp Test

Discussion in 'Reloading' started by Steve Koski, Dec 21, 2011.

  1. Steve Koski

    Steve Koski Got Insurance? Millennium Member

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    I did a home test to test the theory that over crimping actually decreases the case-bullet connection. I made two groups of cartridges, normal and super hard crimp, then I chambered them multiple times in a pistol and measured the change in COL.

    A
    I made 3 rounds with my normal 9mm crimp, once fired Speer brass, 124 grain Xtreme plated bullets, all 1.153" COLs. This is group A. Case mouths all measured .377"

    D
    I turned the crimp die down a FULL turn. Made 3 more rounds. This is group D. D's COLs were less consistent, at 1.155, 1.156, and 1.154. Case mouths measured .366, .366, and .365".

    I then chambered all of the rounds 4 times at approximately 0° (A marking), 180° (B marking), 90° (C marking), and 270° (D marking) (so that the bullet hit the feed ramp at evenly distributed angles) using the slide release, then measured them.

    I chambered all rounds four more times as above and measured again.

    [​IMG]

    [​IMG]

    Notice that the COLs are actually getting a little longer in the group D cartridges. This may be due (in part) to peening the bullet nose and making it sharper. Not sure.

    [​IMG]

    Afterwards I pulled the bullets. 1,2,3 are in group A. 4,5,6 are in group D. It took two decent whacks to pull the group D bullets with the impact puller. The group A bullets all came apart with one decent whack.

    [​IMG]

    [​IMG]

    Conclusion:

    In this test, a "much heavier than normal" crimp significantly increased the strength of the bullet-case connection. Group D bullets resisted setback and the COL actually increased slightly, the cause of which is uncertain. Group A bullets set back in a predictable fashion.
     
    Last edited: Dec 21, 2011
  2. Steve Koski

    Steve Koski Got Insurance? Millennium Member

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    Crimp die setting, looks the same for both A and D.

    [​IMG]

    Mag loading technique, ABCD on top, in an attempt to hit all four sides of the bullet.

    [​IMG]

    Pre-testing pictures:

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]
     

  3. DanaT

    DanaT Pharaoh

    If you look at the bullets, that makes complete sense. Essentially, group A is relying mostly on friction whereas the second group, you have a step. To move beyond the step, you must deform metal.

    The way to really show this, is with a compression test that measures force vs displacement when compressing.

    But essentially, you have made a column instead of a slug sliding inside of a tube.

    But what are you trying to show that is what I am still missing. You haven't shown that over crimping is better, you have simply shown that it resists setback.

    To find the "optimum" crimp would take a more elaborate set-up.

    But I do like this kind of information.

    -Dana
     
  4. XDRoX

    XDRoX

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    I agree, some cool data, but aren't most of us more concerned with accuracy than set back?

    I'd be interested in seeing some accuracy tests with different crimps. Some report that a nice strong crimp can increase accuracy, while I'm sure there's a point in which it hurts as well.

    Anyway, cool post.
     
  5. DanaT

    DanaT Pharaoh

    Lest not forget that the headspace of this cartridge is on the crimp region of the case. Over crmiping can cause additional problems with headspace.

    -Dana
     
  6. Steve Koski

    Steve Koski Got Insurance? Millennium Member

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    Dana,

    In theory over crimping can cause headspacing problems in 9mm, but in the real world it doesn't. In nitrogen rich environments like the earth, cases headspace on the extractor.

    Dana & XD,

    The point was to debunk the theory that over crimping decreases case/bullet tension. It doesn't, at least not in this situation.

    Yes, over crimping could have a bad impact on accuracy. The only rounds I would crimp like this are dummy rounds intended to chamber a bazillion times.

    Koski
     
    Last edited: Dec 21, 2011
  7. DanaT

    DanaT Pharaoh

    I suspect with new brass, that the ammo manufacturers have this data. They want to avoid set back due to over pressure (and being liable) but want to ensure that they maximize accuracy and production lot acceptance.

    I would even wager, that a good guess can be taken in that the crimping should not make the cartridge mouth smaller than 0.373". How did I get that number?

    The cartridge has a SAAMI reference diameter of 0.3800 with no minimum. However the notes say:

    Unless otherwise noted Body diameter -0.007 (0.18)

    [commnet: first dimension is inches, second is mm]

    So, .380-.007 is .373

    Per the drawings of the cartridge, that is probably the crimp range as I can tell.

    -Dana
     
    Last edited: Dec 22, 2011
  8. HAMMERHEAD

    HAMMERHEAD

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    How was the brass expanded prior to seating?
    Expanding and flaring the case mouths?

    I don't expand or flare my auto pistol loads with jacketed bullets and just touch the case mouths with a universal flaring tool for plated bullets, no case mouth expanders used.

    After charging I just seat the jacketed or plated bullet with a competition seating die and skip crimping all together.

    I seem to get the best accuracy this way and I get very consistent set back resistance.

    I appreciate the work, great thread.
     
  9. Steve Koski

    Steve Koski Got Insurance? Millennium Member

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    HH: I flared them in position 2 of my Dillon 550. I took the powder out to protect the children.
     
  10. steve4102

    steve4102

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    How about this?:dunno:

    The bullets in group "A" were set back when they made contact with the feed ramp, barrel hood or whatever. They stayed set back even after the abrupt stop the cartridge makes when it is fully chambered.

    The bullets in group "D" were set back as well, but the poor neck tension caused them to continue forward after the abrupt stop they made when the rounds were fully chambered.
     
  11. GioaJack

    GioaJack Conifer Jack

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    You guys have wwwaaaayyyy too much time on your hands.

    You can't crimp a 9 or 45 enough for it not to fire... although shooting it in the air and actually hitting the sky may prove to be a challenge. Accuracy tends to fall off somewhat. :whistling:

    Fortunately this is not a problem for the young'uns, or Little Stevie since they can't hit the ground with a bowling ball anyway. :faint:


    Jack
     
  12. Steve Koski

    Steve Koski Got Insurance? Millennium Member

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    Too much time on my hands is exactly why I did this test! Christmas vacation baby.
     
  13. steve4102

    steve4102

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    Don't you mean "Winter Break" ?
     
  14. Zombie Steve

    Zombie Steve Decap Pin Killa

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    Interesting. You definitely have a good roll crimp on those.

    I wonder if fmj would make any difference.
     
  15. Steve Koski

    Steve Koski Got Insurance? Millennium Member

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  16. blastfact

    blastfact

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    IMO I think all of your loads are over crimped. And the one's you over crimped are near roll crimps in my book and not good at all in a auto pistol cartridge. Also of note I see only very very slight coke bottle effect in your brass. I use to hate the coke bottle look in my reloads. As I've aged, shot and reloaded. I've come to like the coke bottle effect and all my Lee dies produce it wonderfully.

    I've found the coke bottle and neck tension hold the bullet great! The curve in part of the brass does not let the bullet set back in the brass. I also tend to set my OAL a tad long and enjoy seeing clean extracted brass that shows a good gas seal. I also never have to worry about head space or trusting the extractor will hold the round tight against the breech.

    It's funny I saw this thread. Just last week I got concerned about the ammo in my M&P .45 and PF-9. They have not been shot a lot as of late. But I do keep them loaded with my reloaded SD/HD rounds. And I do check them clean and rotate the ammo around in there mags. I was wondering if I had any set back or pull going on. I measured all the ammo in question. It was all in spec and just as I had made it. And in my mind. I was expecting the 230gn .45 acp's to have a problem because the bullet has so much more weight and a much more agressive slide drop than the little PF-9 be it 124 or 147gn bullets.

    I think what you have proved here is don't do multiple slide racks on plated or lead bullets and don't over crimp them. :) And I myself would never use such a bullet for SD/HD work. :)
     
  17. Steve Koski

    Steve Koski Got Insurance? Millennium Member

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    BF: I am using Lee 9mm dies. The coke bottle effect is what it is. It may be less apparent in once fired brass. Not sure.

    Yeah, plated bullets generally aren't for HD/SD. Unless they are Gold Dots.

    If I crimp my group A rounds any less, you can see a gap between the case mouth and the bullet. .377-.378 = straight wall with this bullet.
     
  18. El_Ron1

    El_Ron1 AAAAAAAAGHHH!!!

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    Some guy with a pocket protector has hacked Koski's account. Uncle Don?
     
  19. Steve Koski

    Steve Koski Got Insurance? Millennium Member

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    Pocket protectors were cool in the 80's. Now it's calcuator watches.
     
  20. Zombie Steve

    Zombie Steve Decap Pin Killa

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    Those never go out of style... like white leather woven belts and shoes.