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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Boosting BC of commerical bullets.....
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<blockquote data-quote="Fiftydriver" data-source="post: 780891" data-attributes="member: 10"><p>The baring surface on the 375 cal, 300 gr Accubond is not a problem, its actually pretty good and does not limit velocity potential at all. Its the new 338 cal version that has a very long baring surface length and that is because they basically only increased the length of the body on the 250 gr version to get the 300 without changing ogive design or boattail design.</p><p> </p><p>In all honesty, I do not think you could do alot with the boat tail to increase BC. Most of the BC is made with ogive design and meplat shape. You would only be looking at an increase in the thousandths range modifying the boattail. You may also weaken the solid base and if the Accubond looses its support cup, penetration will suffer dramatically.</p><p> </p><p>Another issue is consistancy, I have no desire to mess with any part of the rear of the bullet because that is critical as far as accuracy is concerned. In reality, you can get away with more run out on the tip of a bullet then you can if you have run out on the base of a bullet where it contact the crown of the muzzle when fired.</p><p> </p><p>I have tested some prototype 265 gr Aluminum Tipped 338 cal bullets from the old Wildcat bullet company that had very poor aluminum tip run out. At 1000 yards, I tested these in my 338 AM loaded to +3500 fps. One test lot of ammo was loaded with bullets that had tip run outs of less then 0.001". The other test lot of ammo had tip run outs that were all between 0.005 and 0.008". You could see the tips wobble as you rolled them across the loading bench surface.</p><p> </p><p>I shot three, 3 shot groups at 1000 yards on paper and measured group size. The match quality run out bullets averaged 8.890" for three, 3 shot groups at that range. The bullets with poor tip run out averaged 9.783" for three, 3 shot groups at 1000 yards. </p><p> </p><p>So while the poor tips did not shoot as well, at 1000 yards, they shot within an inch group size of the perfect tips...... I was amazed to see this. In my opinion, with a bullet of this mass, a very light aluminum tip will have very little influence if run out is less then 3 thou or so because the mass of the tip is not enough to influence the bullets center of gravity. Remember about the only amount of the bullet that is really out of alignment to any measurable degree is the very tip which weighs virturally nothing compared to the mass of these larger bullets.</p><p> </p><p>Certainly we want everything to be as perfect as possible but having an absolutely perfect tip alignment is less critical then many would ever think. It suprised me!!! The difference is far less then most people would be able to tell down range as enviormental conditions can effect group size much more then a tip slightly off axis. </p><p> </p><p>Now, as far as a boattail a bit off, that would cause serious accuracy issues because one side of the bullet could be released by the crown before the other and the escaping gasses would raise hell with the beginning flight path of the bullet and it would REALLY show up down range with poor consistancy and accuracy.</p></blockquote><p></p>
[QUOTE="Fiftydriver, post: 780891, member: 10"] The baring surface on the 375 cal, 300 gr Accubond is not a problem, its actually pretty good and does not limit velocity potential at all. Its the new 338 cal version that has a very long baring surface length and that is because they basically only increased the length of the body on the 250 gr version to get the 300 without changing ogive design or boattail design. In all honesty, I do not think you could do alot with the boat tail to increase BC. Most of the BC is made with ogive design and meplat shape. You would only be looking at an increase in the thousandths range modifying the boattail. You may also weaken the solid base and if the Accubond looses its support cup, penetration will suffer dramatically. Another issue is consistancy, I have no desire to mess with any part of the rear of the bullet because that is critical as far as accuracy is concerned. In reality, you can get away with more run out on the tip of a bullet then you can if you have run out on the base of a bullet where it contact the crown of the muzzle when fired. I have tested some prototype 265 gr Aluminum Tipped 338 cal bullets from the old Wildcat bullet company that had very poor aluminum tip run out. At 1000 yards, I tested these in my 338 AM loaded to +3500 fps. One test lot of ammo was loaded with bullets that had tip run outs of less then 0.001". The other test lot of ammo had tip run outs that were all between 0.005 and 0.008". You could see the tips wobble as you rolled them across the loading bench surface. I shot three, 3 shot groups at 1000 yards on paper and measured group size. The match quality run out bullets averaged 8.890" for three, 3 shot groups at that range. The bullets with poor tip run out averaged 9.783" for three, 3 shot groups at 1000 yards. So while the poor tips did not shoot as well, at 1000 yards, they shot within an inch group size of the perfect tips...... I was amazed to see this. In my opinion, with a bullet of this mass, a very light aluminum tip will have very little influence if run out is less then 3 thou or so because the mass of the tip is not enough to influence the bullets center of gravity. Remember about the only amount of the bullet that is really out of alignment to any measurable degree is the very tip which weighs virturally nothing compared to the mass of these larger bullets. Certainly we want everything to be as perfect as possible but having an absolutely perfect tip alignment is less critical then many would ever think. It suprised me!!! The difference is far less then most people would be able to tell down range as enviormental conditions can effect group size much more then a tip slightly off axis. Now, as far as a boattail a bit off, that would cause serious accuracy issues because one side of the bullet could be released by the crown before the other and the escaping gasses would raise hell with the beginning flight path of the bullet and it would REALLY show up down range with poor consistancy and accuracy. [/QUOTE]
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Boosting BC of commerical bullets.....
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