Differences in Bullet Types

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  • Differences in Bullet Types

    All,

    I already posted a question about Sierra Pro Hunter bullets. But, sometimes it's all in the way you ask a question. So, let me rephrase to a more general question.

    What is the difffernce when going from a boat tail bullet to a flat bottom bullet?? Every boat tail bullet I shoot using 30.5 grains of AA2520 shoots exceptionally well. But, if I go to a Spitzer / flat bottom bullet, will I be able to use the same charge weight or will the pressure change drastically or something.

    I thought about just loading a few this way and giving it a shot. But, since I'm fairly new to reloading and have been using the same charges in the same bullets ever since I started loading, I feel I don't really have the knowledge or experience to start making educated guesses.

    I am concerned about using the same load that I would use for a boat tail bullet and using it with a flat bottom bullet (never having done that before). I'm concerned that since there is actually less actaul surface material (in a flat bottom bullet) for the gasses to work against, that the pressures may actaully be higher with a flat bottom bullet. My theory here is that a boat tail bullet has more surface area for the gasses to work against since the bullet has a distinct taper. And, the boat tail bullet (in theory) would start moving down the barrel before a flat bottom bullet since there is more surface area for the gases to push against.

    I would appreciate some input from some of the more experience reloaders here. Please let me know if I am even close, or if my theory is a load of crap.
    Last edited by Guest; 08-14-2011, 04:44 AM.

  • #2
    Originally posted by Mutt View Post
    All,

    I thought about just loading a few this way and giving it a shot...snip...
    Whenever you change a component in a load, all else being equal, at a minimum, you drop back 10% and work up again.

    My personal experience has been that a flat bottom bullet, of the same weight, loaded to the same COL, will result in additional powder capacity being made available. Capacity that you are not using. Again, from personal experience, that results in lower pressure and usually lower velocity. Point number one still applies.

    Hoot

    Comment

    • LR1955
      Super Moderator
      • Mar 2011
      • 3355

      #3
      Originally posted by Mutt View Post
      All,

      I already posted a question about Sierra Pro Hunter bullets. But, sometimes it's all in the way you ask a question. So, let me rephrase to a more general question.

      What is the difffernce when going from a boat tail bullet to a flat bottom bullet?? Every boat tail bullet I shoot using 30.5 grains of AA2520 shoots exceptionally well. But, if I go to a Spitzer / flat bottom bullet, will I be able to use the same charge weight or will the pressure change drastically or something.

      I thought about just loading a few this way and giving it a shot. But, since I'm fairly new to reloading and have been using the same charges in the same bullets ever since I started loading, I feel I don't really have the knowledge or experience to start making educated guesses.

      I am concerned about using the same load that I would use for a boat tail bullet and using it with a flat bottom bullet (never having done that before). I'm concerned that since there is actually less actaul surface material (in a flat bottom bullet) for the gasses to work against, that the pressures may actaully be higher with a flat bottom bullet. My theory here is that a boat tail bullet has more surface area for the gasses to work against since the bullet has a distinct taper. And, the boat tail bullet (in theory) would start moving down the barrel before a flat bottom bullet since there is more surface area for the gases to push against.

      I would appreciate some input from some of the more experience reloaders here. Please let me know if I am even close, or if my theory is a load of crap.
      Mutt:

      You are close enough with your theory. However, it really doesn't mean much in real terms. I make and shoot both boat tail and flat base bullets, same weight, same jacket length, same ogive, same loads. I am pretty sure that the flat base bullets produce more initial pressure as there is more bearing surface causing friction. That said, using the same loads, I haven't noticed anything that would make me back off a charge of powder.

      So, as long as you aren't overloading, you won't have a problem. If the flat base bullets are match grade, they will probably hold much more consistent and tighter groups than match grade boat tail bullets -- to about 300 yards. Past that and the advantages of a boat tail take over.

      LR1955

      Comment


      • #4
        Thanks guys. That does make me feel a little safer using these projectiles even though there isn't any specific load data. I've looked through my Sierra loading manual and noticed that most rifle bullets of the same weight are listed side by side with boat tail, spitzer, etc they have the same min and max load data. Guess I'll just have to work some up and see what they do. Thanks for the info.
        Last edited by Guest; 08-14-2011, 04:43 AM.

        Comment

        • LR1955
          Super Moderator
          • Mar 2011
          • 3355

          #5
          Originally posted by Mutt View Post
          Thanks guys. That does make me feel a little safer using these projectiles even though there isn't any specific load data. I've looked through my Sierra loading manual and noticed that most rifle bullets of the same weight are listed side by side with boat tail, spitzer, etc they have the same min and max load data. Guess I'll just have to work some up and see what they do. Thanks for the info.
          Mutt:

          FYI, I just looked at some chronograph data where I compared boat tail and flat base bullets for velocity changes. Again, identical jackets, weight, and ogive. Identical loads using a couple of different powders just to make sure it wasn't powder specific. The only difference was one bullet had a boat tail and the other was flat base.

          The velocity was either equal or tended to be slightly higher for the flat base bullets. That said, the greatest difference I found was only 30 fps and that went to a flat base. I do not consider a 30 fps difference in velocity to be of any significance. In fact, it is just part of the variance you will find day to day and particularly when using chronographs.

          The problem is that bullet companies don't make boat tail and flat base bullets using the same jacket length combined with the same ogive. In this case, I go with Sierra whose reloading manual groups bullets together by weight and not shape. Yes, there are differences but they are of no consequence.

          LR1955

          Comment


          • #6
            According to QL, your 30.5 of 2520 produces about 3K more psi with the Sierra 120gr MK(boat tail) than the 120gr SP (flat base), using the same OAL.

            Comment

            • LR1955
              Super Moderator
              • Mar 2011
              • 3355

              #7
              Originally posted by mseric View Post
              According to QL, your 30.5 of 2520 produces about 3K more psi with the Sierra 120gr MK(boat tail) than the 120gr SP (flat base), using the same OAL.
              MS:

              The problem is that the 120 SP and MK are most likely made with different ogives and most likely the jackets are very different in dimensions and length. I say this because match grade jackets are generally thinner and with a different set of internal dimensions than hunting jackets. If the jacket length and ogive is different between the two, the results will be skewed.

              I don't have Quick Load so wonder if they list the Grendel and if their data is based off of actual testing or just modeling?

              Either way, I guess it is up to a guy to make up his own mind.

              LR1955

              The question is whether or not there is a significant difference in pressure and velocity between a flat base design and a boat tail design.

              That's why you have to keep the jackets, weight, ogive, and loads identical before you can say with certainty that one differs from the other to a degree that means something.

              Comment

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