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case length dimensions and tolerances?

Discussion in '10mm Reloading Forum' started by Kegs, Oct 13, 2010.

  1. Kegs

    Kegs Ol 8 fingers ;)

    Oct 26, 2009
    Cold side of conus
    The precision and point of impact of every firearm I am aware of will change based on how far the bullet sits to the lands.

    As you all are probably aware, this cartridge head spaces on the mouth - but if you are building a cartridge to a specific case overall length (COL) and your cases aren't the same size, your bullets are going to be a different distance from your lands when the move into battery.

    I have noted a vast difference in case length based on the measurements I have been doing with Scharch (top) brass. The short sample I took was that the cases measured from 0.982" to 0.992" with an average of .988". I believe this is going to create an impact on precision - even if the velocity turns a low s.d. through the chrono.

    I do get a round that is off P.O.I. sometimes when everything "felt" right - I am wondering if it a variance in case lengths could set it off enough...

    I noted that in one reloading manual it showed the trim-to length @ .982" with a max length of .992", yet wikipedia suggests .992" as the length of the cartridge and earlier I purchased a LEE trim guide that seems to measure .992".

    Can I get some of you all to measure some of your formed cases (please state the brand) to get a comparison?

    Do you sort cases for length to make precision loads to ensure the bullet is in the sweet spot - or is the .01" variance not worth messing with?
    Last edited: Oct 13, 2010
  2. Taterhead

    Taterhead Counting Beans

    Dec 13, 2008
    Boise, Idaho
    Great questions. I have wondered if the cartridge actually does headspace off of the case mouth, or if it is kind of held in place to some degree by the extractor - with the case mouth sitting ever-so-slightly from fully seated. I wonder if this is especially true in a semi-sloppy Glock. I don't know if a Glock setup really has noticeable differences between .982 & .992". I am no expert, but this is what I suspect.

    From reading your various posts, you are probably more tuned into getting the last ounce of precision from your rounds than I am. A lot of folks are more accurate than I am. That being said, I haven't found my loads to be a limiting factor on accuracy. I am admittedly a bit less accurate than any of the loads I shoot.

    Bottom line: I do not worry at all about brass length as long as it is within specs. Now rifle is another story. Case prep is, for me, far more critical for rifle. But then I like to shoot longer ranges, and I am looking for very consistent velocities. Carefull case prep pays off when sending lead at 3/4 of a mile. At the distances that I shoot pistol, I am just not as concerned.

    One thing I have found that has had a noticible effect on accuracy is crimp. I had a loads that seemingly few around like frisbies (I'm exagerating but you get he point) with really bad fliers here and there. After pulling a few, I noticed that I had WAY over crimped to the point of disturbing the bullet shape. Under crimping with slow powders like A9 have noticeable increases in velocity SDs. At longer distances, this would likely affect accuracy at longer distances.

  3. crsuribe

    crsuribe 10mm Auto

    Jul 3, 2010
    I love Kegs' threads. There's always so much information in them and we all get to learn some.

    I have nothing to contribute here as I don't even have the calipers but just wanted to drop in and say thanks for yet another interesting 10mm-related thread.
  4. anomad


    Jan 9, 2003
    I'm living out of a storage unit that is 400 miles away or I would be happy to measure a few sized cases. I do have some different (re)loaded ammo with Starline brass. I am not sure how the seated/crimped bullet would affect OAL.
  5. Hogpauls


    Nov 6, 2009
    Thanks Kegs, I never think of this stuff until I read your threads. Here you go, 6 random Starline and Winchester all sized through RCBS carbide sizer (don't know if that makes a difference).

    Starline Wall Winchester Wall
    Thickness Thickness
    .987 .012 .990 .012
    .988 .012 .986 .013
    .988 .012 .985 .013
    .988 .012 .984 .012
    .988 .012 .988 .014
    .988 .012 .984 .012

    I'm glad I went with the bulk Starline over the Winchester. I was pretty surprised at the variances the Winchester exhibited.
    ETA. I can't get those numbers to look like I want, you'll get it though.
    Last edited: Oct 16, 2010
  6. Kegs

    Kegs Ol 8 fingers ;)

    Oct 26, 2009
    Cold side of conus
    That is very consistent. .988" is the average of all of my cases, but the variance is more along the lines of Winchesters.

    I am going to start sorting my brass by length and weight. The lighter weight brass are getting bright marks on them around the case mouth.

    I suppose I could tone the load down some, but I don't want to do that. :supergrin:

    Also...The next brass I buy are going to be double tap nickel plated. After tumbling around 500 or so brass a couple of days ago, after I was going through cleaning and inspecting them, I noticed that the nickel plated had a LOT less dents on them and were far easier to clean off than the yellow stuff. I suspect they will last longer and take more power too.
    Last edited: Oct 16, 2010
  7. Taterhead

    Taterhead Counting Beans

    Dec 13, 2008
    Boise, Idaho
    I'm pretty sure that DT nickle is Starline nickle so it should be good stuff. I think Starline only sells nickle in commercial quantities otherwise the price may be better than at DT. I think I remember seeing Starline nickle @ Midway for prices better than from DT. You may want to check it out.

    Nickle cases are harder so they are a bit more abusive to your carbide resizers. You can really feel more resistance when pulling the lever. I've also noticed that they have different expansion characteristics than plain brass. They seem harder and less maliable than non-plated brass. I don't know if more power is attainable or not. My gut says that if they are harder, then they may be prone to splitting earlier than regular brass. I haven't loaded max stuff side-by-side to compare. It has been an either/or situation.

    I'd love to see your results though.