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Bullet Length Effects Theory

Discussion in '10mm Reloading Forum' started by preventec47, Jun 9, 2010.

  1. preventec47


    May 2, 2010
    Atlanta, GA
    I am attaching a portion of Hornady's 4th edition loading data
    for their 200gr bullets both hollow point and the shorter non-hollow
    point what I like to call solid since it aint hollow.

    It is not always good to make assumptions but for the sake
    of this message making a point, I'd like to assume that since
    both bullets are made by Hornady they would have same diameters
    and jacket construction and jacket material etc.
    The same cases and primers and powders are used as well.

    Take a look at the AA7 and AA9 loads ( the only two that
    are appropriate in terms of burn speed vs bullet weight )
    using the same weight bullet and notice the
    difference in performance, psi pressures and
    amount of powder used.

    As far as I can tell the only reason for loading data
    differences here is the very small difference in bullet
    length and the effect on usable case capacity
    and the resulting effect on bore pressure.

    What I see is that the shorter bullet has higher
    velocities because of being able to use more powder
    because of the lower pressures.

    This is why I have become so sensitive to bullet length.

    What other conclusions can be drawn ?
  2. ctkelly


    May 9, 2010
    The weight of the bullet will have a direct effect on the amount of pressure that can be safely generated also. If it were as simple as just having more powder room I would load a 200 grain XTP out long for my 610 revolver and shoot it at velocities the 135 noslers can achieve....but it doesn't work this way.

    Now of course...assuming same weight, jacket design, etc...then yes a bullet that is shorter in length will free up powder space which in turn will lower pressure. However you typically then have to compensate with more powder to achieve the same velocity. Many have found this to be true when working with the 10mm magnum.

    There is merit in what you are looking at however.....if you take a look at the barnes XPB bullets which are all copper alloy, they are relatively long compared to other bullets in the same weight due to the difference in density of lead vs copper. However they will still fly faster than an equivalent length traditional lead core bullet, say 180 or 200 grains because of the difference in weight and pressure produced.

    Quickload will show you the pressure curve, where peak pressure occurs, and if combustion is completed before or after the projectile leaves the bullet. Now quickload isn't the bottom line when it comes to things, like anything it makes certain assumptions and isn't 100% accurate...but for intents and purposes it does a pretty good job.

    This post is going to seem like a bunch of rambling since its early in the morning and I keep adding stuff...

    To get the shortest bullet with a hollow point in a given weight, the ogive is going to have a big part in this as will the size of the hollow point. Ogive will affect the feeding process, size of the hollow point will dictate its ideal velocity for expansion. The base of the bullet will also come into play...the GDHP in 155 grain has a dished or hollow base which will free up some room. However the size of the hollow point is rather large, even if it is bonded......I believe the GDHP has a problem withstanding top velocities and Mike McNett loaded these slightly lower than an XTP in equivalent size.
    Last edited: Jun 9, 2010

  3. ctkelly


    May 9, 2010
    Hmm something to throw out there for your database...

    155 Grn silvertip, .550 in length
    155 GDHP .546 in length
    165 Precision Delta .546 in length

    What I find interesting is the construction of the 155 GDHP and the 165 Precision delta FP. They are both the same in length, but the delta is 10 grains heavier of course. It also has a similar base construction....the GDHP is dished and completely covered, the delta has the core exposed at the base but it is not flat with the is in fact dished slightly like the 155 GDHP. The ogive is very different however between the two, as long as they feed reliably this wont affect much.

    Then we get to the silvertip vs the GDHP. The gold dot has a large hollow point, but the cavity is rather shallow. The silvertip starts out with a large opening then has a smaller hole bored through deep within the bullet. The silvertip also has a flat base as opposed to the dished base. The ogive is similar but slightly different.
  4. preventec47


    May 2, 2010
    Atlanta, GA
    Last edited: Jun 9, 2010
  5. preventec47


    May 2, 2010
    Atlanta, GA
    you have reminded me of a flaw in my presentation of bullet length.
    The simple technique I illustrated assumed
    flat bases that would allow for simple
    calculations of space displaced in the case.
    Where we have bullets with dished bases
    and those whose jackets are rolled around
    the edge with a depression for the visible
    lead base, we would have to compensate
    a little to arrive at an "effective" bullet length
    for purposes of the calculation.

    Actually I think it would be pretty easy to
    get real close. Take micrometer and measure
    the longest part of the bullet. That would
    in all pistol bullets that I know of be to the
    outside rear edge of the bullet. ( dont know
    of any boattail pistol bullets)

    Then take a round ball, something like a BB
    and mike the distance from the bullet nose
    to the end of the BB that is placed in the
    rear depression of the bullet. Then just take
    the average of those two lengths after
    subtracting the BB diameter and we should
    be real close to an accurate usable number
    for length to use.
    Last edited: Jun 9, 2010
  6. ctkelly


    May 9, 2010
    Actually I think I will bow out from your discussions from now on. I think you need to stop asking everyone (that includes the 6-7 other forums you have been trampling all over lately) to do testing for you and go out and do it yourself. In all the posts in various forums I have yet to see you actually post something about results of any load development or testing you have done so far....just a lot of theories and opinions.
  7. preventec47


    May 2, 2010
    Atlanta, GA
    I am a little disappointed in the accuracy and childishness
    of your comments but thanks for the bullet length info
    and other contributions along with the dialog and advice.
    The length info was used to update the main list.

    "Trampled" huh. Great word choice.
  8. _The_Shadow

    _The_Shadow Ret. Fireman

    Jul 23, 2007
    Southeast, LoUiSiAna
    I'll throw this out ther to make a point about the different length bullets...

    What some have failed to realize is that the longer bullets have more frictional gilding metal surface area to resist being spit out of the barrel. This extra surface area(ever so slightly more) with the increase friction raises the overall pressure in addition to the space for powder being smaller to also increase presures more rapidly.

    Now stuff them long boys in your pipe, then smoke'm if you wish!:smoking: