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Old August 15, 2012, 11:19 AM   #26
Bart B.
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dacaur, go back and read my post again. I think you misread or misunderstood it.

What I said was that with both bullet types being perfect and zero spread in BC, muzzle velocity and atmospheric conditions (nothing in the air changes for all shots fired; it's all constant), both types will shoot with the same accuracy. But the FB bullet's group will be lower on the target than the BT one 'cause it drops more due to its lower BC.
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Old August 15, 2012, 04:30 PM   #27
tobnpr
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This seems to make sense to me, but I'm no engineer. Just seems "logical".
See "First"...

http://www.appliedballisticsllc.com/...lletDesign.htm
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Old August 15, 2012, 08:39 PM   #28
dacaur
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Quote:
dacaur, go back and read my post again. I think you misread or misunderstood it.

What I said was that with both bullet types being perfect and zero spread in BC, muzzle velocity and atmospheric conditions (nothing in the air changes for all shots fired; it's all constant), both types will shoot with the same accuracy. But the FB bullet's group will be lower on the target than the BT one 'cause it drops more due to its lower BC.
I have never been much interested in theories. (which is what the above is.) Real world testing has shown over and over that the BT is going to be more accurate than the FB at long range, no matter how calm conditions are or seem. There is no point in saying "but if conditions are identical and perfect..." because they never will be. Car makers use a similar theory to figure the MPG on the new car sticker, and well all know how accurate that is.

So even with both bullet types being perfect and zero spread in BC, muzzle velocity and with real world atmospheric conditions (as opposed to theoretical) Yes the FB bullet will be lower on the target at 1000 yards, but it will also have much bigger groups, every time, because everthing that has affected the BT bullet on the way to the target, has affected the FB bullet MORE (excluding gravity, of course)
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Old August 15, 2012, 08:54 PM   #29
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Given equal BC and launch speed of flat base and boat tail bullets there is no advantage in the boat tail bullet's trajectory until after it has dropped below sonic speed.
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Old August 16, 2012, 09:32 AM   #30
Bart B.
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wncchester, what boattailed bullets stay accurate after they've gone subsonic? I'm not aware of any, nor any flat based ones, either.
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Old August 16, 2012, 03:15 PM   #31
wncchester
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Bart, I wasn't addressing pure accuracy, only the slightly flatter trajectory at the longer ranges after the bullets drop below sonic speeds. But some people translate their inability to properly correct for drop as 'better accuracy' with boattails.

Me, I'm a practical southeastern hunter and I've never detected any predictable differences in accuracy directly due to the form of the base but then I'm really not a long range shooter anyway. I've only been doing this stuff since '65 so I still have a lot to learn!
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Old August 16, 2012, 03:48 PM   #32
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This has been interesting reading. I didn't know the answer, so I hoped that ya'll would come up with one. What I have read over the years, and what I have come to believe (right or wrong) is that a flat base or a boat tail, if constructed equally well, will shoot equally well. However, it seems that a flat base bullet that has a perfect (or nearly perfect base) is easier to produce than a boat tailed bullet with a perfectly tapered base. Because of that, it's more likely that a flat based bullet will leave the muzzle 'squarely', whereas a boat tailed bullet with a less perfect base (or boat tail) will be slightly more inclined to leave the muzzle less than squarely due to unequal gas pressure acting on the imperfect boat tail as the gas and bullet escape the muzzle.

More than likely, today's bullet production quality allows for more perfectly shaped boat tails than in previous years and previous decades, so maybe this is no longer an issue. If so, they should shoot equally well in properly crowned barrels.
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Old August 16, 2012, 05:00 PM   #33
Bart B.
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wncchester, as far as I know, all bullets, regardless of their shape at the back end, change direction somewhat when they go from supersonic to subsonic. That's why Lake City ammo plant quit using Sierra 168's in their 7.62 NATO match ammo; they went subsonic around 800 to 900 yards and accuracy was deplorable at 1000. Sierra's 175 HPBT replaced the 168 and its longer boattail keeps them supersonic through 1000 easily. That's also why the US Army changed to a 173-gr. FMJBT bullet in the 1920's for the .30-06 long range machine gun use; the 150 spitzers in standard ammo too often went subsonic before reaching 1000 and their accuracy wasn't what Uncle Sam wanted.
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Old August 19, 2012, 06:56 PM   #34
rivertrash
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The bullet is only one component of a cartridge and like everything else, if the rifle doesn't like it then accuracy is out the door. I have a Remington 300 win mag that simply does not like ANY boat tail bullet. You have to experiment with all components with each gun to find the best load.
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Old August 20, 2012, 08:09 AM   #35
Bart B.
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Quote:
You have to experiment with all components with each gun to find the best load.
That's true if one tests rifles to find out "what they like" by firing a couple of few-shot groups. Most any combination of components will end up shooting the smallest one.

On the other hand, there's several companies making centerfire match ammo that shoots great in decent rifles when properly tested by competant people. Lake City Army Ammo Plant's been doing that for decades with their 7.62 NATO match ammo. And Federal's Gold Medal Match stuff been the commercial industry standard for just as long.
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Old August 20, 2012, 09:06 AM   #36
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So im kind of confused. Bart I hear and agree with everything you are saying but as one person commented before, they thought given the BT and FB at a far range the FB would hold less of a grouping. Besides the obvious drop, would wind resistance not affect the FB because of the streamline capabilities. Even if there is no wind, would there not be resistance in the air on matter how minimal. For instance, an object cutting through water, depending on the streamline capabilities would slow it down but could it slightly change direction? I am unsure but is there not always resistance... besides gravity of course.

Sorry if this is completely wrong, its been a long time since physics in college, im just trying to brainstorm if the poster could in someway be correct. Also could this be tested if you found a way to take a 1000yrd shot indoors, say the largest airport hanger. Would that not eliminate wind?
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Old August 21, 2012, 06:39 AM   #37
Bart B.
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themaliciousone, bullets in flight won't change direction (other than what gravity and spin drift from gyroscopic precession causes) unless some external force makes them do so. Both flat base and boattail bullets that are perfectly balanced will repeat their trajectories exactly for every shot when muzzle velocity and atmospheric conditions are constant for each. One bullet types group will be at a different location than the other, but both would be the same size. All's well until they slow down and start traveling at the speed of sound. That's when an external force causes problems because all bullets are not perfectly balanced.

Saved some time ago from some web site:

Quote:
When the velocity of a rifle bullet fired at supersonic muzzle velocity approaches the speed of sound it enters the transonic region. In the transonic region, an important thing that happens to most bullets, is that the centre of pressure (CP) shifts forward as the bullet decelerates. That CP shift affects the (dynamic) stability of the bullet. If the bullet is not well stabilized (a perfect spiral football throw), it can not remain pointing forward through the transonic region (the bullets starts to exhibit an unwanted coneing motion (wobbly football throw) that, if not dampened out, can eventually end in uncontrollable tumbling along the length axis). However, even if the bullet has sufficient stability (static and dynamic) to be able to fly through the transonic region and remain pointing forward, it is still affected. The erratic and sudden CP shift and (temporary) decrease of dynamic stability can cause significant dispersion (and hence significant accuracy decay), even if the bullet’s flight becomes well behaved again when it enters the subsonic region. This makes accurately predicting the ballistic behaviour of bullets in the transonic region very hard. Because of this, marksmen normally restrict themselves to engaging targets within the supersonic range of the bullet used.
I feel that if one could shoot only perfectly balanced bullets out of their barrels, they would be more accurate after going subsonic. But one needs to spin them at rpm's they leave at then measure their out of balance and set aside the perfect ones for shooting; all without damaging them so they could be shot such that they wouldn't be unbalanced going into the rifling.

Start shooting on the range half an hour before sunrise; it's often dead calm then and the air's so still and stable you can see bullet holes in the black at 1000 yards with a decent spotting scope.

Last edited by Bart B.; August 21, 2012 at 11:01 AM.
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Old August 21, 2012, 08:59 PM   #38
dacaur
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Quote:
So im kind of confused. Bart I hear and agree with everything you are saying but as one person commented before, they thought given the BT and FB at a far range the FB would hold less of a grouping. Besides the obvious drop, would wind resistance not affect the FB because of the streamline capabilities. Even if there is no wind, would there not be resistance in the air on matter how minimal. For instance, an object cutting through water, depending on the streamline capabilities would slow it down but could it slightly change direction? I am unsure but is there not always resistance... besides gravity of course.

Sorry if this is completely wrong, its been a long time since physics in college, im just trying to brainstorm if the poster could in someway be correct. Also could this be tested if you found a way to take a 1000yrd shot indoors, say the largest airport hanger. Would that not eliminate wind?
In theory? "maybe"...... But most of us dont shoot in theory, we shoot in real life, right? And of course in real life you have to take real life variables into account.... Even pretending we have an imaginary "windless day" there are variable which can, (and always do), cause the BT's groups to open up less at long range. Seemingly innocuous things like varying terrain that changes from grass to sand and back is going to have an effect, since the air will be warmer over the sand than the grass, which in itself would still lend uniformity to groups, except that its not just warmer, but rising, which means its being replaced, with air from over the grass, which then needs to be replaced, etc.... so, you have swirling air, even on a windless day.... unfortunately for this particular "theory", its not going to swirl uniformly, so each and every bullet has a different pattern of air density to go through. Thats going to affect every shot, but as we know, its going to affect the boat tail bullets less, and the FB bullets more, so the FB bullets groups will always open up more than BT bullets groups, even on a mythical "windless" day.




BTW, the largest hanger in the world is something under 400 yards, and even if one were built 1000 yards long, its going to have windows, which means its going to have temperature variations along the flight path.....
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Old August 22, 2012, 06:44 AM   #39
Bart B.
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Dacaur, you're right. The air moves around. I like to watch it when its speed is well under 1 mph so I can make adjustments and correct for it. That's the speed range when it's easiest to see the small, subtle changes. Sometimes its hard to decide if its movement changed enough to make a 1/8 minute change on the sights when the air's barely moving.

Unfortunately, one can only see the wind moving in one range band at a time. So one has to decide if they want to see the wind's movement near the target, somewhere between target and you or near you. But it's the wind nearest you that has the greatest effect. It's impossible to observe the wind at all distances at the same time between muzzle and target. And it's harder to see it on cool days compared to warm ones.

Last edited by Bart B.; August 22, 2012 at 08:13 AM.
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Old August 22, 2012, 09:29 PM   #40
dacaur
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I'm not saying you have to see and adjust for it at every part along the flight path, that of course just isnt possible. I'm just saying that its there, and it IS going to affect your bullets flight, and since its not constant like gravity, its going to affect each shot differently, regardless of if its a BT or a FB bullet. Obviously due to its lower B.C., its going to affect the FB bullet more. (A bunch of little random pushes from random directions), which means the FB groups are going to open up faster than the BT groups as range increases. Thats what this whole thread is about....
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