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Fat ain't where it's at...it's BC...

Discussion in 'Rifle Country' started by Jasper1573, Jan 17, 2013.

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  1. Big JJ

    Big JJ Member

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    Helotaxi/Team
    So two bullets shot out of the same gun with all other factors being the same except the lead vs copper bullet the lead will stabilize better than the copper???
    When I load copper I use Barnes bullets and Barnes load data.
    When loading lead I use load date that will give me the same FPS to match the Barnes FPS and the powder or bullet mfg formulas.
    When I put the 200 grain lead next to the 200 grain copper bullet the copper is noticeably longer.
    My gun is a Remington model 788,308win with a 1 to 10 twist.
    The copper always shoot a better group off of a bench rest than my lead bullets.
    I always thought it was due to the length of the bullets and there ability to stabilize in the air.
    Given the facts you have stated above it makes me think that I should be looking for other ways to increase the accuracy of my lead bullets.
    What do you guys think???
     
  2. helotaxi

    helotaxi Member

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    Stability and accuracy are not the same thing. Bullet consistency and matching the powder charge and bullet to the barrel harmonics as well as barrel quality determine accuracy for the mast part, but that assumes that the bullets is stable. For the bullet to be stable in flight, it must leave the muzzle without excessive yaw (mostly a barrel and bullet quality thing) and be spinning fast enough to be gyroscopically stable. The longer the bullet, the faster it must be spun to be stable. As long as the bullet is stable, that's all you really care about from a practical standpoint. There are some that argue "degrees of stability" but for all practical purposes, it's a binary question "is the bullet stable or not?"

    Matching velocity between two completely different bullets is usually not the formula for getting one to shoot as well as the other. If you can get them stable, the Barnes bullets often can shoot very well simply because they are very consistent. You don't have issues with jacket thickness inconsistencies or the bullet imbalance that they can cause. They usually have a fairly long bearing surface and that means that they will usually enter the bore straight. All of these things are very conducive to getting very consistent results from shot to shot. On the other hand, some rifles have an inadequate rate of twist to get the longer monolithic bullets stable or leaves them right at the ragged edge. Unstable means that you'll likely never hit the target, while marginal stability usually ends with very inconsistent accuracy.
     
  3. d2wing

    d2wing Member

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    A bullet of greater diameter will have more rotational enertia and well as longitudinal enertia. So just scaling down a bullet doesn't work. Actual bullet engineers know that their are optimal shapes, sizes and weights that consider all factors. As hello said, much depends on quantity of the bullet, seating in relation to lands and optimal load for each design bullet.
    Making a bullet longer for the same mass makes it less stabile as a general rule if it is already at optimum length.
    In the case of the copper bullet, it also could be that the more consistent weight distribution as lead bullet the cog is behind the midpoint of the bullet. Also the bullet could engage the lands sooner as it is longer. I dunno.
     
    Last edited: Jan 21, 2013
  4. d2wing

    d2wing Member

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    I am sorry, what I said is about maximum ranges. Helo is right about scaled down ranges. There are optimum efficiencies at scaled down ranges. Bench rest shooter are striving for these goals and have down a wonderful job of refining the optimum caliber projectiles, speed twist rates, and many other factors such as quality of components, chamber and cartridge, primer, each variable carefully developed for the range to shoot at. It is not about maximums but optimums and quality control. Neither fat or skinny is a good rule of thumb. Refinement is.
     
  5. Big JJ

    Big JJ Member

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    d2wing and Helo
    Thank you for clearing up some of my assumptions.
    I am considering casting my own bullets in 308 and 357.
    I would like to get the most consistant range rounds that I can get.
    It looks like Lee mfg is the best bullet mold maker that I can find at resonable price. That is currently my choice. I am open to suggestions.
    What do you guys consider to be the optimum bullet grain weight and shape for the these two calibers and what should the best FPS be for the best accuracy.
    This seems to be a mathmatical problem that I have no idea how to solve.
    There are obverously more issues to consider than than the 3 I have asked about above however it does seem to me that there should be a optimum bullet for the two calibers.
    Maybe there is a data base for this type of info that I should be looking at???
    Maybe just use the info from a bullet mfg and take the bullet with the highest BC for the caiber???
    Thanks Big JJ
     
  6. RPRNY

    RPRNY Member

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    JJ - optimal bullets will depend on YOUR rifles. Ballpark optimal is somewhere around the longest that will consistently stabilize out to the range you desire and, if used for hunting, deliver optimal terminal ballistics, ie controlled, optimized expansion. This will in turn be determined by powder charge - type of powder and amount - as this will determine velocity and terminal ballistics at a given range.

    I would suggest that before buying bulllet molds, you buy a selection of the most likely bullets cast from the molds you are looking at (Montana Bullet Works, Oregon Trail, Beartooth etc., to name but a few suppliers) and that you develop some loads (Lyman always has good cast data) to see what is working well for you in your rifles. THEN buy the molds.

    You may also want to go http://castboolits.gunloads.com/forum.php and http://www.castbulletassoc.org/for example to do some more research.
     
  7. d2wing

    d2wing Member

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    With cast bullets high BC isn't an issue because you can't push them real fast anyway as far as I know. I did cast 357 bullets years ago and used a luber sizer and gas checks.
    As I recall I used a Elmer Keith hot .38 load and a Semi wadcutter bullet design.
    Casting .308 is way over my pay grade. As Rprny said you need to see the guys that know.
     
  8. Big JJ

    Big JJ Member

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    Team
    Thanks for the advice..
    I am sure that it has saved me a lot of headaches.
     
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