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What is the sweet spot for 10mm crimping?

Discussion in '10mm Reloading Forum' started by 21Carrier, Apr 9, 2011.


  1. 21Carrier

    21Carrier
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    While setting up my new RCBS 10mm dies (carbide 3-die set), the instructions said to set the crimp as follows: After seating a bullet, measure the case just about .25" from the mouth of the case (not all the way at the top, but about where the base of the bullet is inside the case). Then, measure the case right at the mouth (very top of the case), it should be equal to or slightly less than the diameter of the first measurement. Well, I have mine set so that my two measurements are .421" at base of bullet, and .4215" at the case mouth. This is basically equivalent (as per the instructions), and I tried turning or pushing the bullet back into the case, but it feels very secure.

    I'm just thinking that maybe I should crimp it a little more. I'm more worried about developing sufficient pressure to achieve complete combustion, as set-back seems to be a non-issue. I've measured bullets after cycling them several times vigorously, with no set-back. What do you guys think?
     

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  2. _The_Shadow

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    It sounds like you have it set fairly close...

    I set my RCBS taper crimp to see that the case mouth gets a little shine on the brass and the taper is starting. But the most important thing is that the bullet not move in or out or spin inside the casing.

    I seat the bullets to proper depth without any crimp aplication, I use a 1/8" spacer ring to lift my seater/crimp die up so i don't have to fidle with the crimp setting each time. Adjust the seater stem for proper COAL and seat all of the rounds, then remove the spacer, screwing the die down to the set locking ring, back off on the seater stem and crimp them all.

    Also be aware that your brass can shorten up over many resizings.
     

  3. nickE10mm

    nickE10mm
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    tell me again WHY exactly this is... ?
     
  4. _The_Shadow

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    The staright walled cases tend to get shorter over many resizings, unlike rifle cases where the neck sizer has the tendancy to draw the neck back increasing their length some.
     
  5. Taterhead

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    When brass is rammed up through the resized die, it acts like a compression force. There is no offsetting stretching force like occurs when firing bottle neck cases. As The Shadow mentioned, the up stoke of re-sizing bottle neck cases also imparts a bit of stretching force too.

    The number one reason I toss brass is because it shrinks below minimum specs.
     
  6. 21Carrier

    21Carrier
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    I had always thought (and read from countless sources) that brass gets LONGER when sized. I had always thought that was counterintuitive, but I trusted the pros. I have not yet bought a case trimmer, and always measure my brass to be sure. I have only noticed shortening, no lengthening. I guess that only applies to rifle brass. Great, that means I don't need a trimmer.
     
  7. Taterhead

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    Thousands of rounds of pistol brass through my press. All of them have shrunk over time. Rifle brass requires trimming - so I would be really surprise if you ever use the trimmer.
     
  8. 21Carrier

    21Carrier
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    Thanks, man. That just saved me at least $50-100. I don't shoot or reload rifles (right now), so I'll put the money towards something else.
     
  9. nickE10mm

    nickE10mm
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    Thanks Shadow and Taterhead...

    I knew they shortened but had forgotten WHY they did so. Since I only reload 10mm (so far) I didn't have any bottleneck cartridges to compare the effect to. Compression was kinda what I figured but it's good to know for sure.

    Seems like too short a case could create a dangerous headspacing condition.
     
    #9 nickE10mm, Apr 24, 2011
    Last edited: Apr 24, 2011
  10. Taterhead

    Taterhead
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    When the time comes to load rifle, I'll save you some more money. Lee makes a nifty gauge and trimmer that works with any drill (I use it with my cordless drill). It is only about twelve bucks and works very quicky.
     
  11. 21Carrier

    21Carrier
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    I would think a short case would just allow the cartridge to seat too deeply, and be out of reach of the firing pin. It seems like failure to fire would be the worst of it.
     
  12. Snapper2

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    Doesn't brass stretch to the chamber size when fired? And in unsupported areas stretch a little more. This shortens the brass of course. But when resized it brings the brass closer to the original length. That doesnt mean the brass shrank in size. If put through a full length sizer and pushed through it probably gains in length. Or is my understanding off again?:embarassed:
     
  13. Kegs

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    ^ This.
     
  14. DWARREN123

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    I set mine so the cartridge will barely fit into the chamber and fall out when turned upside down.
     
  15. Taterhead

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    The force of ramming up a case into a re-sizer compresses the brass from mouth to case head. With a length of pastry dough, rolling out the middle to will cause the umbound edges to increase in length. However, a re-sizing die works by ramming downward on the case. Essentially working brass slightly toward the case head in one direction. Eventually over the course of several reloads, that small amount of downward work causes straight wall cases to shrink. If a re-sizer pulled a case through head first, I imagine that it would lengthen a case. Is there such a product?
     
  16. Snapper2

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    Tater, I see your point. But only because this compression doesnt reach the case head,right? I've taken a Lee push through die which using the body of the factory crimp die, but used instead a RCBS sizing die which sizes the 45acp to .466 which is tight. Then cut the top off the sizing die so the brass will push completely through. My brass lengthens .005-7 when pushed through compared to regular sizing. Maybe the rim is being distorted by .007 during the push through?:dunno:
     
  17. Taterhead

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    I think you might be on to something the with the push through setup. I haven't experimented with those.
     
  18. 21Carrier

    21Carrier
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    AWESOME idea!!! I'm gonna try that instead of buying the Lee setup.

    BTW, what did you use to cut it? Did you have to take it to a machine shop or something? I'd imagine that steel is pretty tough.
     
    #18 21Carrier, Apr 27, 2011
    Last edited: Apr 27, 2011
  19. Snapper2

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    Not too awesome of an ideal. If you use a push through, youre better off using the lee setup.imo. It wont size the brass as much. Size the brass then use a LFCD to push brass through(if you even want to go that route). Probably safer not doing it. I used port a band to cut the top off my sizing die. Hacksaw will work also. The carbide ring is at the bottom.
     
    #19 Snapper2, Apr 27, 2011
    Last edited: Apr 27, 2011