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Old February 10, 2007, 10:17 PM   #1
Blacktail_Slayer
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Advantages of boat tail?

What are the specific advantages of boat tail bullets?
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Old February 10, 2007, 10:28 PM   #2
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all else being equal, they fly flatter longer.
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Old February 10, 2007, 10:34 PM   #3
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Yeah, the streamlining from that bit of taper lowers the drag. It doesn't make much difference in the usual hunting distances, but is greatly helpful for long-range target shooting. It shows up as you get beyond 400 yards, mostly.
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Old February 10, 2007, 10:39 PM   #4
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They are easier to seat when you hand load.

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Old February 10, 2007, 11:27 PM   #5
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Boat Tails

1. Flatter trajectory.

2. Improved "Yaw" (tumble) once hitting soft tissue initiating fragmentation, causing heavy damage by creating a larger temporary wound cavity.

3. Improved stability against cross winds.

4. Reduces drag on the bullet.
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Old February 10, 2007, 11:41 PM   #6
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2. Improved "Yaw" (tumble) once hitting soft tissue initiating fragmentation, causing heavy damage by creating a larger temporary wound cavity.

3. Improved stability against cross winds.


ok, i would really like to understand the logic behind the above two comments.
references appreciated.
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Old February 10, 2007, 11:53 PM   #7
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Quote:
1. Flatter trajectory.

2. Improved "Yaw" (tumble) once hitting soft tissue initiating fragmentation, causing heavy damage by creating a larger temporary wound cavity.

3. Improved stability against cross winds.

4. Reduces drag on the bullet.
* Number 4 is the cause, number 1 is the effect, so let's not get confused.

* Actually, boat tail bullets do not yaw as easily, because their center of gravity, or center of mass if you prefer, if closer to the center of the length of the projectile. Bullets with heavier bases than noses yaw more easily. This is why most dangerous game bullets are rather blunt.

* Number 3 is accurate, because the center of gravity of the bullet is closer to the geometric center of the bullet. A flat based bullet's center of gravity is farther back than half its length, allowing side forces to more easily deflect the bullet's point in flight. The forward portion of the bullet is tapered, therefore contains less metal. This is also a reason why spire point bullets do not fly as well as curved ogive bullets.
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Old February 11, 2007, 06:06 PM   #8
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* Actually, boat tail bullets do not yaw as easily, because their center of gravity, or center of mass if you prefer, if closer to the center of the length of the projectile. Bullets with heavier bases than noses yaw more easily. This is why most dangerous game bullets are rather blunt.

ok. the next 3 times I'm killing an elephant, i'll not take boattails. however, by the same logic, shooting deer with reasonably size ammo means tumble would be a good thing.

* Number 3 is accurate, because the center of gravity of the bullet is closer to the geometric center of the bullet. A flat based bullet's center of gravity is farther back than half its length, allowing side forces to more easily deflect the bullet's point in flight. The forward portion of the bullet is tapered, therefore contains less metal. This is also a reason why spire point bullets do not fly as well as curved ogive bullets.

Hold a boattail and a spitzer up in the air crosswise to the wind. the boattail will have less leverage exerted by the wind at the tail. but the boattail will have a lower polar moment of inertia then the spitzer, so the spitzer should hold its straightness.
otoh, the spitzer has a larger tail, which means the wind will push the back of the bullet around more, therebye encouraging the bullet to actually fight the wind.

All of this is mouse testicles. I suppose the Boattail tends to have a lower coefficient of drag, meaning it is in the air less time, therebye has less time to get blown around.
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Old February 11, 2007, 06:44 PM   #9
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Good answer FS2K

It just looked like some other people wanted to bust your chops - to make it look as if they had the right answer too.. You just beat them to it.
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Old February 11, 2007, 06:58 PM   #10
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I always thought a boattail was the streamlining of a spitzer bullet but I see in the manual that the combination offers the best of both worlds it would seem: a higher BC of (0.540 - .308" 180 gr 30BT Spitzer-SP versus 0.483 - .308" 180 gr 30 Spitzer-SP) than most others making it a pretty darn good long range bullet shape.

When a boattail bullet travels, a vacuum is created when air strata moving at high speed passes over the end of a bullet. The streamlined boat tail design aims to eliminate this drag-inducing vacuum by allowing the air to flow alongside the surface of the tapering end, thus eliminating the need for air to turn around the 90-degree angle normally formed by the end of shaped bullets. (wikipedia)

You guys really do make me do my research. Thanks

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Old February 11, 2007, 07:04 PM   #11
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BT are fine for long range shooting, but may not be as accurate as short, flat base bullets for short distances, i.e. <200 yards...It SOMETIMES takes the BTs a longer distance to get stabilized, or "go to sleep". Not always, but sometimes. Note that most benchrest shooters shoot flat based bullets.
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Old February 11, 2007, 07:16 PM   #12
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Hilton

The boat tail reduces the effect, but doesn't get rid of base drag. The only way to get rid of it is fill the base drag area with gas, ala the Fumer effect.

Perfect case in point the M864 BBPICM round can get a out to around 28 KM because of the base burn unit. While its brother the M483 can only go around 23KM because of the lack of the gas generator in the base.
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Old February 11, 2007, 11:53 PM   #13
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Quote:
Note that most benchrest shooters shoot flat based bullets.
Yup, it's interesting that discussions of boat-tail bullets rarely bring up the disadvantages. Another one is increased bore wear. Like the accuracy difference, it's probably not a significant issue for the vast majority of shooters.
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Old February 12, 2007, 12:56 AM   #14
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Quote:
The only way to get rid of it is fill the base drag area with gas, ala the Fumer effect
I'd like to find out more about this effect. Could you direct me to a resource?

I was only thinking about 600 - 1000 yards but 23 kilometers will do.

Quote:
Another one is increased bore wear. Like the accuracy difference, it's probably not a significant issue for the vast majority of shooters.
Why would there be an increase in bore wear? Does the bullet wobble in the barrel slightly due to the shape until it leaves the muzzle? What would you suggest the lifespan of the barrel would be then?

Just curious.

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Old February 12, 2007, 02:26 AM   #15
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Well Thanks Gamemaster.

I just wanted to help answer the Slayers question. LOL!

Quote:
2. Improved "Yaw" (tumble) once hitting soft tissue initiating fragmentation, causing heavy damage by creating a larger temporary wound cavity.

3. Improved stability against cross winds.


ok, i would really like to understand the logic behind the above two comments.
references appreciated.
#1. Yaw. Take a look at the construction of a Boat Tail bullet. The inner core of the bullet isn't shaped like the jacket around it. There is an air "pocket" within the pointed tip of a boat tail round created using the jacket material. I really wish I could draw a picture of this, as it is lengthy to explain. Anyway, after the pocket is the inner core itself. A Boat tail bullet does not carry its center of mass in the middle of the bullet, it is carried slightly to the rear.

Upon contact with soft tissue the tip of the bullet collapses and the jacket material begins to peel away. (**IF the bullet has enough velocity behind it) In the meanwhile the main body of the bullet wants to continue moving forward in a straight line but is interrupted by the collapsing front of the round. This causes the bullet to start to Yaw; the rear of the bullet attempts to overtake the front and begins to topple, end over end. The added length of the bullet design causes the energy of the round to dispurse quickly as it tumbles which in turn causes a larger temporary wound cavity to occur as well as spreading fragmented pieces outward & away from the main mass of the bullet.
The shorter the bullet (full metal jacket/ball ammo), the less likely it is to tumble. It can occur, but whats more likely to happen is the bullet ceases to travel in a straight line and turns, IF anything at all. The reason is that regular flat based/non boat-tail rounds do carry their weight more centered and lack the air pocket in their noses like the boat tails made for AR15's.

While the "Boat-tail" end of the bullet design is what helps the bullet stabilize in flight, it's the hollowed out pocket of air just beneath the tip that initiates the wounding effects of the bullet.



#2. The Cross-wind issue.

Reference: AR15.com "the Ammo Oracle" http://www.ammo-oracle.com/body.htm

Quote: "BT stands for "Boat Tail" and refers to the base of the bullet. A "Boat Tail" is a sloping end which narrows gently at the base of the bullet, so that the cross-section resembles the shape of a boat's hull. The boat tail shape reduces drag on a bullet, helping it to retain velocity and resist deflection from crosswinds, but causes the bullet to take longer to "settle" after leaving the barrel compared to a standard "flat-base" bullet. Boat tail bullets are usually selected for long-range shooting, while the flat-base bullet shape tends to be more accurate at short ranges. A "HPBT" bullet is a "Hollow Point Boat Tail" bullet."
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Old February 12, 2007, 11:28 AM   #16
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why is it that the front of the bullet for a boattail by definition is much different then a flat based bullet?

in other words, you imply you cant make a "tumbler" flat base. Why?
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Old February 12, 2007, 11:38 AM   #17
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I did NOT imply anything.

Why is the tip of a boat-tail bullet different? Well, like I said several times the point of the BT is HOLLOW. There is an Air pocket there that isn't usually present in 'regular' jacketed bullets. The tip of the core in a BT bullet does not extend to the very top of the inner jacket. In 'regular/common' bullets it does; the jacket simply follows the shape of the core.

And as for tumbling, I said:

Quote:
The shorter the bullet (full metal jacket/ball ammo), the less likely it is to tumble. It can occur, but whats more likely to happen is the bullet ceases to travel in a straight line and turns, IF anything at all. The reason is that regular flat based/non boat-tail rounds do carry their weight more centered and lack the air pocket in their noses like the boat tails made for AR15's.
The Air pocket in the tips of BT rounds are there for a reason. They collapse upon impact and disrupts the forward momentum of the bullets, and initiates the fragible effect of the thin jacketed bullet.

Imagine a bicycle rolling downhill in a straight line, then someone stuffs a stick in the spokes of the front wheel. The momentum of the bicycle is inturrupted and the mass behind the front wheel pivots around the center axis of the wheel causing the bicycle to flip over end over end.

Now imagine a bicycle rolling along on a flat, horizontal surface, but this time the bicycle has a much shorter wheelbase. The same thing happens; someone stuffs a stick into the spokes of the front wheel. However the bicycle does not flip end over end, instead it slows very rapidly and the chassis becomes unstable, but unless the rider leans forward the bicycle does not flip. It may still crash, but flipping over becomes more difficult to do.

The downhill angle represents the areodynamic shape of the boat-tails bullets effect on the bullet in flight/ and the longer stretched out shape of the bullet and it's tapered end. It helps the bullet cut through the air more stabilly thus allowing better utilization of the energy behind them. (more stability at higher velocity)

The stick in the front wheel represents soft tissue and how it effects the bullets forward momentum. For the BT design it also represents the effects of the tip of the jacket collapsing as it contacts the soft tissue.

The longer bodied BT bullet WILL cause a larger temporary wound cavity opposed to a shorter flat base bullet because the action of it flipping end over end disturbs more of the air around it. (in the case of the bullets, flesh.) Even if it too were to flip end over end, the shorter bullet still wouldn't disturb as much of its surroundings as the longer bullet would. (Like the shorter wheel based bicycle)
The jacket of a Fragible BT bullet is also designed (thin) to peel away and break apart easily once hitting soft tissue, causing further damage to its surroundings. The thicker jackets of non-frag rounds hold their shape better and do not.

I've tried to attempt to answer the issues you've brought up with what I've said as best I could Miller. Have a good day.

There are definate characteristic differences between these types of bullets INCLUDING the tips of their jackets and how they react upon impact.
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Old February 12, 2007, 11:48 AM   #18
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All spitzer rounds and probably all jacketed rounds with a closed nose have an air pocket, the pocket may be very small but it is still there. The air has to go somewhere when the round is swagged.
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Old February 12, 2007, 12:47 PM   #19
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True, however....

Not all jacketed rounds are designed to fragment, which is the key reason for the Air pockets function on a BT fragible round.

Granted, there are some BT bullets that are ineffectual as fragible rounds not because of a lack of the Air pocket formed by the bullets jacket, but because the metal used to make their jackets are too thick, and won't peel apart as expected. But for the most part, QUALITY BT rounds do fragment reliably.
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Old February 12, 2007, 01:39 PM   #20
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I think you are confusing multiple types of projectiles. A frangible is a round specifically designed to disintegrate when it hits steel or other very hard objects. They are made of with bonded particle and gilding material, to insure they break into non-hazardous or low hazard pieces when they hit a hard target. These are normally are only used in training, however some units SOP has them change to the round prior to doing an entry to reduce penetration hazard.

Spitzer rounds all yaw when they hit dense substances. It is an effect of the center of gravity being quite a way behind the ogive. Yawing tends to increase the severity of the wound by creating a larger permanent wound cavity. The question is when and where the certain projectile tends to yaw, some do very quick and some won't till you go through the equivalent of several human torsos. Many spitzer rounds fragment, but that was a positive side effect and until recently not by purpose of design.

A larger air pocket would actually be a negative for yawing since it causes the center of gravity to be father back. The Soviets by placing a steel kicker behind the lead get around this. Steel causes the lead in front of it to flow forward asymmetrically on deceleration, exceleration yaw. The Soviets wanted the yaw of their 5.45 round to occur inside the body. Many think this is because of an incorrect belief that the claimed great lethality of the M193 round used in Vietnam was because of yaw (tumbling) rather than the later understood fragmentation following yaw.
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Old February 12, 2007, 05:08 PM   #21
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Boat Tail Bullets do not "increase barrel wear"

"Boat Tail Bullets Decrease Barrel Life" is a myth.

As long as the bullets have a good gas seal then the only thing causing wear is the amount of metal to metal contact between bullet and steel, the "sandblast effect" of unburnt powder on the throat, and heat checking.

Someone back in the day though that the boat tail end would cause the hot gasses to "cut the grooves" like the "flames of a welding torch" which is why he "only used flat based bullets". If you have a proper sized bullet this cannot happen.

If you have an undersized bullet, then this "welding torch" effect would happen EVEN WITH A FLATBASED BULLET.

Maybe this myth got started because long range shooters use boat tail bullets and change their barrels out so often. Who knows.

Anyways it is time for this myth to die.

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Old February 12, 2007, 06:44 PM   #22
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I remember some text books from when I was a Gunnery Instructor that mention the swirling of gas around base of the boat tail led to increased wear.

Also gas erosion is a greater cause of tube wear than the friction of the projectile going up the tube. In the AM2 TFT there are tables to determine wear per round fired. The same round shows almost no measurable wear if fired in conjunction with Green Bag, but while fired with White Bag or Red Bag causes much more wear.
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Old February 12, 2007, 08:25 PM   #23
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Sometimes military explanation should be taken with a grain of salt. When I asked a chemical corps major if 2PAM was a "treatment or a cure" he said, "I don't know, the material refers to it as both". I asked him how it worked an he didn't know. Had to find out for myself in a medicinal chemistry textbook how pralidoxime works. It's an SN2 reaction displacing the carbophosphate inhibiting the acetylcholinesterase surrounding neural synapses.

Drill Sergeants are still teaching recruits to "only pull the trigger with the tip of the finger".

I'm not saying the military is always wrong, only that the military doesn't have a monopoly on correct answers.

Anyways, to the issue at hand. All the evidence supports heavier charges cause heavier wear. This is caused by higher temperatures and pressures. The "gases swirling around the base of the projectile" explanation would work if and only if the wear was drastically worse for boat tail projectiles.

If you fired a flat base projectile with heavier charges you also see increased barrel wear.

When a primer ignites it ignites the powder at the rear of the cartrige. This builds pressure that pushes the unburnt powder and the bullet forward. The bullet stops and starts again as it engages the lands. The unburnt powder is "sandblasting" the throat, the pressure is building to it's highest "peak" and this is the worst things are going to get.

In a 308 the rest of the powder doesn't finish burning until the bullet has passed 18 to 20 inches of barrel. If the swirling gasses really caused such wear we should see barrels that fire boat tails exclusively to have measureable damage all the way down the bore. This is not the case. In "tactical" rifles the heavy wear portion of the rifle is the throat. In fact many shooters still order a barrel long so that they can have it cut back and rechambered to get a "new" barrel.

And as far as barrel wear on Artillery pieces, I know some gun bunnys that confessed to throwing a coffee can of sand in with the last round. Said it made the bore "shiney clean".

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Old February 12, 2007, 08:40 PM   #24
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True, the military teaches some wives' tales along with some facts. But BRL created allot of our source material. There are still and other photo showing the swirling effect of gas going around boat tail. The swirls of gas are supposable responsible for the increase wear.

We have long since abandoned flat base projectiles in order to get the max range out of our guns, so I don't think they have looked at what happens between charges with a flat base vice boat tail arty round.

Bore wear is a very, very important in predictive gunnery. Starting with Paulkowsky and Bruckmueller in WWI Artillerymen have preferred pull over gauge readings, but when not available we will take into account rounds fired and wear caused by the Equivalent Full Charges (EFC) of those specific charge.

An Art 15/NJP would be appropriate for someone adding anything to the powder train, this will change the point of impact of the round, and could cause a firing incident.
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Old February 12, 2007, 08:58 PM   #25
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That would be true...

Quote:
A larger air pocket would actually be a negative for yawing since it causes the center of gravity to be father back. .
Yes STLRN this is true: But for a bullet that retains it's shape after impact. As I mentioned, the collapsing tip serves as a braking force while the main mass of the bullet pushes from behind. The energy of the projectile wants to continue on a straight path, but now that its leading edge has drastically slowed the momentum of the bullets mass has nowhere to go but around the nose in an attempt to continue moving forward....A tumble.

If the point of the bullet remains intact the bullet will react like a nail being driven into wood; a pointed leading edge punching its way forward with its mass pushing it from behind.
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