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How much crimp?

Discussion in '10mm Reloading Forum' started by robert91922, Jun 18, 2012.

  1. I had few jams on feeding ramp w. my 212gr hardcast ammo:
    (post No.3 on 5th page)
    Looking closer at latest jams I found out that rounds have too much brass edge on the top or better said they were not crimped enough. Rounds are 0.420 wide in the middle but at crimping point (the edge) I measured 0.423 or 0.4225. I adjusted crimping die and fixed the crimp to 0.420. Bullets are hardcast HB23 hardness so I don't expect any pressure increase due to a bit narrower end of case.
    This week I will chrono them again anyway just to see if there are any signs of overpressure or change of speed.

    In the meantime, all my other ammo (jacketed or plated) works flawlessly, so should I set back crimping to 0.423 or leave it on 0.420 for future use when I spend all of the rest of my 212gr hardcast bullets?
    Last edited: Jun 18, 2012
  2. Minnow


    Jan 13, 2006
    I measure the case at/near the base of the bullet after seating said bullet in the case. I then crimp to match this measurement with the 10mm Auto. That is usually .420"-.421", so you are on the right track. All you are doing is removing the bell in the case so using the above method will give you the correct measurement.

    Another method for taper crimp is brass thickness X 2 plus bullet diameter, but I prefer the method I listed first. .423" is max case mouth OD, and as you found .425" resulted in feed jams.
    Last edited: Jun 18, 2012

  3. None of them was .425 at the crimp edge, they were from .4225 to .4230
    Tomorrow I will measure speed and look for any other issues including those jams. This evening I will fix the crimp to .420 also on some 200grXTP/1250fps rounds and test them tomorrow as well.
    Last edited: Jun 18, 2012
  4. dm1906

    dm1906 Retired SO

    Sep 7, 2010
    PRK (Kalifornia)
    Case mouth crimp with the components you are using should not be an issue, within min/max spec. A relatively slower powder, such as N105, allows for some flexibility.

    .420" case mouth taper crimp, a maximum of .421" behind the mouth, and a maximum of .425" at the rim and web, is the right standard to set for any 10mm. The case wall from web to mouth should taper, and have no greater diameter outside the taper at any point. The maximum diameter of the chamber is .424" at the mouth, and .4281" at the breach (SAAMI). The closer you get to the actual chamber dimensions, the more critical it becomes for cartridge staging alignment. Glock OEM accommodates this with a relatively deep feed ramp, and the reason we full power shooters seek aftermarket chambers. A much more shallow (or nearly non-existent) feed ramp and case web relief creates an even more critical condition. If the case mouth and crimp is too wide, the cartridge will have a difficult alignment during chambering, which increases with a more misaligned staging. Tighter chamber dimensions make bullet meplat, ogive radius or taper angle, and crimp diameters more critical. Any chamber interference during chambering can, and often does, lead to feed issues. A round may "drop" into a chamber, and seem to be rather "loose" when seated in the chamber, but still have interference issues when chambered into action during a firing event. The cartridges you have pictured appear to have sufficient ogive radius and meplat to accommodate a tight chamber, so that leaves the case diameter(s) that may have caused your FTF issue.

    IGB offers 2 chamber options. One is Glock OEM, and the other only specifies use for full power loads. They don't list the actual dimensions.
  5. Minnow


    Jan 13, 2006
    Sorry, hadn't had my coffee yet when I seen that number. My advice stands. If you still got problems after a .420" crimp, then the crimp is not the problem.
    Last edited: Jun 18, 2012
  6. Taterhead

    Taterhead Counting Beans

    Dec 13, 2008
    Boise, Idaho
    Good to see that you got things working for the hardcast bullets Robert . For plated, I would recommend no less than 0.422" of crimp so as not to bite into the plating. I have found that groups get sloppy when the plating is disturbed. I believe that you use Starline brass (if I recall correctly) so your measurements should be consistent with mine.

    At 0.420", I have observed that jacketed bullets will have a pronounced ring etched into the bullet. I have also noticed that it can be somewhat asymmetrical too where one side is engraved more than the other. I can't imagine that is preferable for promoting good groups. I have found that 0.422"of crimp is just about eight for jacketed bullets when using Starline brass.
  7. In the meantime I have found out that it's not a crimp related issue, I presume my mag springs to be weakened due to high summer temperatures and even more due to be loaded full -1 almost all the time last 2 years
    FTFs happen only w. my hottest load e.g. 212gr/1230fps, 200gr/1250fps, 165gr/1400fps, 195gr/1250 fps and 180gr/1330fps in the beginning every 3rd load but it's getting worse as outer temp is rising (every 2nd or even every)
    When shooting weaker or better said mild loads like 180gr/1200fps or 200gr/1100fps I have no FTFs, it works flawlessly.
    I will post pictures of jams and more explanation in a new thread related more w. weakened mag springs and very hot 10mm loads.
    (scroll to the top)
    Last edited: Jul 1, 2012