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Old 02-19-2009, 05:31 PM   #1
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Default boat tail question?

I have a question about an ammunition designation: Boat tailed--I would assume it means that the rounds base is slightly narrower than the middle which contacts the neck of the case (like a boat). My question is: What is the advantage (if any) of boat tail ammunition? I though maybe it was to shave a few precious grams off the weight of the round. I was just curious cause some of my 5.56 for my AR is boat tail and I have some other rounds that aren't.



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Old 02-19-2009, 06:12 PM   #2
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Boat tailed bullets are tapered at the base of the bullet. This helps in aerodynamics.



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Old 02-19-2009, 06:49 PM   #3
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Dragunov - Basically the boat tail is as you assume, having a tapered rear end.

The modern rifle bullet was initially designed to increase the distance on the battlefield. I believe it was the Spitzer Bullet, but it didn't feature the curved, boat tail shape, somewhere around the late 1890's if memory serves.

Somewhere along the way some egghead figured out that there was a problem with air moving along the bullet and then having a 90 degree angle at the back of the bullet. This created a vacuum, which affected trajectory, distance and a few other things.

By adding the "boat tail" design, it increased the distance and accuracy of the same bullet.

Thus, for long range shooting, the boat tail design was adopted and the world was a much better, and deadlier, place to be because of it.

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Old 02-19-2009, 07:08 PM   #4
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What they said. The primary disadvantage to most boattail designs is they have a tendancy to shed their jackets more easily on larger game. many hunters of elk sized game and larger opt for flat base to minimize the possibility of shedding the jacket and losing mass, thus reducing penetration.

Some of the modern bonded core designs should stay together better and allow proper penetration.

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Old 02-19-2009, 07:16 PM   #5
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I once heard that boat tail bullets shoot better than a spitzer in heavy cross winds because the center of gravity is more toward the center of the projectile rather than at the back resulting in a striaghter trajectory.

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Old 02-19-2009, 07:23 PM   #6
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"My question is: What is the advantage (if any) of boat tail ammunition? "

Actually, all other things being equal, a boat tail does nothing until the bullet velocity drops below the speed of sound. (about 1,150 fps, IIRC)

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Old 02-19-2009, 07:26 PM   #7
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Quote:
Originally Posted by 1hole View Post
"My question is: What is the advantage (if any) of boat tail ammunition? "

Actually, all other things being equal, a boat tail does nothing until the bullet velocity drops below the speed of sound. (about 1,150 fps, IIRC)

What's the thinking on that? Just out of curiosity?

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Old 02-20-2009, 12:41 AM   #8
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"What's the thinking on that? Just out of curiosity? "

Well, I hate to write long things (ain't too good at it), but I'll try.

Most of us understand that bullets of the same ballistic coefficent and same velocity will have, supposedly anyway, the same trajectory wheither it's a boat tail, hp, bt, etc, or not. The critical thing to rember for this to make sense is "the same BC", not the same caliber or weight!

The "vacuum" which forms behind the base of a speeding bullet serves to retard it's flight just as surely as does the forward resistance of the frontal area. The cross sectional area of any bullet is normally what determines the actual power of the vacuum's drag effect. A boat tail has a smaller base area but that advantage doesn't come into play until the bullet drops below the speed of sound.

So long as the bullet is supersonic, the air pressure breaks from the jacket at either the heel, a flat-base bullet, OR at the step down, a boat-tail. That means both types have the same "vacuum" pull down to that speed. But below sonic speed, (about 1,150 fps if memory serves) the air follows the boattail's step until it reaches the heel of the boattail before it can break away at the smaller base. Since that reduced base's cross sectional area is much less than full diameter the drag effect of the vacuum on a boat tail is suddenly lessened, but it only happens below that critical speed.

Or so the ballistics experts say, I can't run fast enough to watch.

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Old 02-20-2009, 12:58 AM   #9
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Thanks for that explanation 1hole. That was something that I did not know.

JD

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Old 05-31-2009, 06:19 PM   #10
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Default Boat tails versus vlat bottom bullets

Hi All,
As said above, a boat tail bullet tends to go faster due to reduced drag, and therefore has a flatter trajectory.

I cannot speak for other makes, but I personally use Hornady Interlock bullets
( 180Gr) for my 3006, and have hunted with it KUDU, ORYX, Warthog, Springbuk and impala in several occasions. ( a close friend of mine used it with his 30-06 on Eland as well)

I have seen optimal performance both with the flat bottom and with the boat tails, and I am not aware of any tendency of boat tails to shed their jackets.

It is important to note the velocity when bullets do not perform well. I know of several cases where bullets hitting animals at very high velocities have broken of separated from the jackets.

Regards,
Danny



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