Case capacity

Discussion in 'Reloading' started by lever-hed, Jul 21, 2009.

  1. lever-hed

    lever-hed Well-Known Member

    May 8, 2008
    Do any of you guys measure case capacity and what is your thought on how this really affects pressure/accuracy. My reasoning is that I hear this and that all over about measuring case capacity and how it can affect accuracy – I figure it really has no place in my regiment because 50.2 grains of powder is still 50.2 grains of powder, regardless of capacity. Well, density maybe is one way of looking at it, but still this is only a “measurement” on the case and should really not matter. I have no place for this kind of time waster for my reloading .:)
  2. AJ Peacock

    AJ Peacock Well-Known Member

    Oct 7, 2005
    I measure the case capacity of new brass, so I can compare to future lots. If a new lot has more capacity than an old lot, the same amount of powder will have a slightly lower velocity than the old lot. If the new lot has a lower capacity, the same amount of powder will have a higher velocity and HIGHER PRESSURE.

    For me, it is easy to measure a few brass each time I get a new lot of brass. After all my brass prep, I will quickly weigh all the brass and segregate any that are really heavy or really light (in comparison). I even measure the capacity of the heavy ones and light ones, just to denote it in my log book.

    I like to know everything possible about my reloads. By keeping this kind of detail, I'm pretty confident within 1/2moa out to 800yds on 3 of my rifles.


  3. Mikecr

    Mikecr Well-Known Member

    Aug 10, 2003
    You declared conclusion with inquiry......

    But you're wrong in ascertion that powder amount as a factor stands independent of it's confinement.
  4. boomtube

    boomtube Well-Known Member

    Oct 8, 2007
    "Do any of you guys measure case capacity"

    I did, at one time. Don't now and haven't for maybe 30 years.

    "and what is your thought on how this really affects pressure/accuracy"

    Not much.

    Yeah, sure it does affect pressure, some, and that MAY affect accuracy, at least a little. It will affect safety IF your load is already smoking an occasional primer pocket. Actually, IMHO, it's mostly anal agonizing over what's largely trivial. After all, while capacities do vary a bit, it's NOT a massive difference as some make it sound. Case differences are NOT going to blow up anything if the load is a safe one to start with.

    Accuracy? Test it yourself. Accuracy is found within a range of powder charges that may wlll be .5 gr. or more wide, not a specific point, +/- nothing. Use carefully matched cases and load five in the middle of your loads best range, then load another five with the same charge but using cases with differenct head stamps. Shoot them iwth equal care.

    You will then see how much difference normal case variations make to YOU! It may be as much as 10%, or even less. If so, your hoped for 3/4" groups (.75") become .825" groups; worse by a shade over 1/16th inch? And, since that must be split in half as the decrease in accuracy from the point of aim. it becomes about 1/32th inch worse. Whould that make the time measuring case capacity worthwhile? Not to me!

    A 10% improvement, or whatever small amout you may find, difference mean nothing to a deer or ground hog and precious few crows. And, of course, it makes some difference in any competition shooting, especially long range.

    I do segregate (most) of my ammo by brand and keep track of how many times it's been reloaded. And that's it, these days. (I learn slow but I do learn!)