Whats The Advantage of a Boat Tail Projectile?

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Beyond 1100 fps @ sea level, the bullet shock wave parts the airflow anyways. It super cavitates the air. It is no longer aerodynamic until it slows back below the speed of sound.
Humor me o_O

I'm not entirely sure what your post is saying, but boattail bullets have a higher ballistic coefficient than the same diameter and weight flat base. That translates into a flatter trajectory and less wind drift. That is proven, not theoretical.
 
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Boat tail bullet Advantages
FMJ-BT Advantages. The whole purpose of the FMJ-BT was to provide a more stable flight and increased accuracy. This is done by tapering the end of the bullet, causing an increase in the ballistic coefficient. Today, most shooters demand the accuracy of the boat tail design, as it out-performs designs of the past.

Remember to factor in wind drift as well as flatter shooting at longer distances. IE retaining velocity better from the better BC
 
Beyond 1100 fps @ sea level, the bullet shock wave parts the airflow anyways. It super cavitates the air. It is no longer aerodynamic until it slows back below the speed of sound.
Your information is wrong. If it were true jet fighters could travel at 3X the speed of sound with no aerodynamic concerns.

A real world example. A modern 180 gr boat tail bullet with good aerodynamics fired from a 30-06 @ 2800 fps is moving FASTER at only 75 yards than a 180 bullet with poor aerodynamics fired from a 300 WM at 3000 fps. The same aerodynamic bullet fired from a 308 at 2600 fps will pass the 300WM at only 175 yards.
 
Beyond 1100 fps @ sea level, the bullet shock wave parts the airflow anyways. It super cavitates the air. It is no longer aerodynamic until it slows back below the speed of sound.
Humor me o_O

Aerodynamic? That has no technical meaning except for defining the enrie field of study. All objects going through the air are subject to aerodynamic forces.
Do you mean laminar? Smooth air, traveling along the surface of the object. Because that's still not quite right. When the air settles it just becomes still, as there's nothing moving through it we care about anymore.

Anyway, trying to do it without math, the empty tail of a bullet (or your pickup truck, etc) causes a low pressure zone behind the projectile. Air cannot get into if fast enough so it detaches from the bullet surface. Detached air is turbulent, and draggy. Drag is bad. Reduces your range. Posting Taliv's image here to illustrate:
2ddb3ac178a01ec5d0a3b76065dba66d.jpg https://i.pinimg.com/originals/2d/db/3a/2ddb3ac178a01ec5d0a3b76065dba66d.jpg

See the twisty air coming off the back? That's bad.

The boat tail is very simply a taper. It starts the air flow moving the right direction for the flat back. Too steep of a boat tail and the flow would become non-laminar anyway. So, these angles are very carefully designed, and tested. Look REAL close at the photo and you can see a bit of turbulence coming off the middle of the boat tail on the bottom. This is right at the edge of the taper being too much, probably because the bullet operates over a very large range of velocities, and you cannot design it for all of them. Here it may be going too fast for optimal performance, and in a bit it'll settle down.

(Yeah, things like less accuracy up close are not an illusion, the bullet changes how it flies as it changes speed going downrange).

And note the flat is not cut off clean, but the end of the boat tail has a radius to taper into it. All this reduces the degree to which the air is disturbed by the back of the bullet.

Some larger projectiles (artillery I mean) add a small propellent charge to the back of the shell. This "base bleed" fills that empty space behind the shell with pressurized gas, and effectively is a big long tail to the bullet. This is not a rocket, it provide no thrust, just gets rid of the low pressure zone. And it works so well that you can get 30% more range from a 155 shell. So, the empty space is a hell of an impact to the aerodynamics of the system!

Boat tails also will be less disturbed by the removal of the shock wave and transition to entirely pressure based aerodynamics when you get to extreme range. Past supersonic ranges, flat tail bullets have much, much higher dispersion than boat tails so once they drop subsonic, that's your effective range. Boat tails can stretch a bit further as their airflow continues to be smooth so they are not so disturbed by the velocity threshold change.
 
Your information is wrong. If it were true jet fighters could travel at 3X the speed of sound with no aerodynamic concerns.

A real world example. A modern 180 gr boat tail bullet with good aerodynamics fired from a 30-06 @ 2800 fps is moving FASTER at only 75 yards than a 180 bullet with poor aerodynamics fired from a 300 WM at 3000 fps. The same aerodynamic bullet fired from a 308 at 2600 fps will pass the 300WM at only 175 yards.

I am also a pilot since age 16. Jet fighters or any SS airframe do Not have separate stabilizers and control surfaces for one simple reason, that's because the aerodynamic forces disappear beyond Mach I. The craft would no longer be controllable. The Fully movable surfaces used on SS aircraft simply deflect the shock waves beyond SS speeds. That being told, boat tailed projectile has NO aerodynamic effect on the bullet at all. The boat tail is over hyped as more aerodynamic. It's sorta like peeps that prefer Ford over Dodge. The advent of boat tail bullets had a psychological impact on the populous they look cool and so the people without true aeronautical knowledge 'believe it' and pay more for them. Good for corporate gurus pocket books.
 
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I'm not entirely sure what your post is saying, but boattail bullets have a higher ballistic coefficient than the same diameter and weight flat base. That translates into a flatter trajectory and less wind drift. That is proven, not theoretical.

higher ballistic coefficient of What! Ballistic Coefficient (BC) is basically a measure of how streamlined a bullet is; that is, how well it cuts through the air. Mathematically, it is the ratio of a bullet's sectional density to its coefficient of form. Ballistic Coefficient is essentially a measure of air drag. ... Both increase the BC of a bullet.

Bzzzzt! WRONG. Super Sonic Bullets are NOT aerodynamic at all....
 
"... boat tailed projectile has NO aerodynamic effect on the bullet at all."

Steelangel, your view is opposed by the known fact that the trajectory of a boat-tail is flatter than that of a flat-base. That can only occur due to a lesser rate of loss of velocity from air resistance.

A different milieu, but pertinent: https://en.wikipedia.org/wiki/Kammback

I vaguely recall that the "chop-off" point was where the tail is one-third of the cross-sectional area at the midpoint of the car.
 
"... boat tailed projectile has NO aerodynamic effect on the bullet at all."

Steelangel, your view is opposed by the known fact that the trajectory of a boat-tail is flatter than that of a flat-base. That can only occur due to a lesser rate of loss of velocity from air resistance.

A different milieu, but pertinent: https://en.wikipedia.org/wiki/Kammback

I vaguely recall that the "chop-off" point was where the tail is one-third of the cross-sectional area at the midpoint of the car.

hahaha, it's not a car, lolol.. The drag created by a SS bullet is created by the initial shock wave cone itself, not air flow. Same goes for crosswind drift = angle of the shockwave cone as related to the relative wind. I also debunked Ballistic Coefficient that I posted above for SS bullets. Again No airflow over the SS projectiles my men. Hey, I used to love loading those Hornady BTHP's in the 80's, I thought they were hot stuffs, but as my aero knowledge progressed, I realized it was all a crock. Time for a Ted Nugent video ;)
 
I like boattail bullets for two reasons. They load easier into the neck of the case, and they have less bearing surface inside the barrel which can increase velocity without increasing pressure. In years past I liked long bullets but in my quest for accuracy and performance in a hunting rifle I now favor shorter boattail bullets. The 150 grain boattail out of a 30-06 at 2900 fps is a good example. Easy to load, accurate and hit like a hammer.
 
I like boattail bullets for two reasons. They load easier into the neck of the case, and they have less bearing surface inside the barrel which can increase velocity without increasing pressure. In years past I liked long bullets but in my quest for accuracy and performance in a hunting rifle I now favor shorter boattail bullets.
Now those reasons I can buy, but the aerodynamic reason some swear by are baloney. Thanks for the feedback! :)
 
All other factors equal, a boattail bullet has a higher ballistic coefficient, i.e., less drag that a flat base, for the reasons others have stated. This results in a longer, flatter trajectory.

The other benefit is that the bullet drifts less in a crosswind. Try a flat point 30 caliber bullet in your ballistic calculator, and then try a spitzer boattail of the same weight, at the same speed, in the same crosswind. The flat point will have much greater deflection.
 
I like boattail bullets for two reasons. They load easier into the neck of the case, and they have less bearing surface inside the barrel which can increase velocity without increasing pressure. In years past I liked long bullets but in my quest for accuracy and performance in a hunting rifle I now favor shorter boattail bullets. The 150 grain boattail out of a 30-06 at 2900 fps is a good example. Easy to load, accurate and hit like a hammer.

^^^^^ Yea, that! For some reason, apparently in error, I have always felt that boat tail bullets were more aerodynamic, maintained less friction in the barrel due to less surface area in contact. That they hold together better on contact with game. They are easier to seat in the case neck.
I'm a bit surprised the data doesn't support the data that boatails aren't all of the above contentions... Where else do shooters and reloaders get their info from, albeit with a grain of salt (?).....from gun writers.

Objectively, I have found boatails to be more accurate for me. I experience less wind drift. I rarely use full throttle loads, or chase maximums. And now days I don't shoot past 300 yard on the range or the field. However, boatails are what I prefer.
 
The Whitcombe Area Rule was determined so that we would know that to reduce the number and power of shock waves generated in transonic and supersonic flow, an aerodynamic shape should change in cross-sectional area as smoothly as possible. By the area rule, we can know that two bullets with the same longitudinal cross-sectional area distribution will have the same wave drag, independent of how the area is distributed laterally. Don't confuse this independence in lateral distribution with a indifference to cross-sectional area. In bullets, unlike aircraft, we have axially symmetric shapes without wings because we've opted for spin-stabilization and compatibility with the bore rather than trying to generate lift. To avoid the formation of strong shock waves, the area distribution must be smooth. The reason for gradually reducing the diameter of the tail rather than having a square tail is because it does indeed reduce wave drag. We can see this wave-drag reduction exemplified in the Sears–Haack body.

There might be some merit to the idea that amateur ballisticians have a misconception about the boat-tail being there to lower viscous pressure drag rather than understanding its effect on wave drag, but supersonic bullet design is not lacking in the application of wave-drag principles. That's why we see Haack-style ogives and indeed boat-tails. We typically don't see anything approaching the theoretical Sears-Haack shape, because there are other practical trade-offs. It has taken a remarkably long time just to start seeing a shift to VLD-compatible cartridge designs, frankly because .308 was good enough for what had been expected of it. That isn't to say that there aren't opportunities to dramatically improve wave-drag conditions for supersonic bullets. I mentioned this already in another recent thread where I suggested that it was possible to sound-suppress the shock waves from supersonic bullets. I actually expect most of the innovation in this area will happen earlier in rail gun projectile design because of those programs are pushing 12,000fps and have super-computer budgets, and importantly, the systems are novel and the market doesn't expect them to be backward compatible with 19th-century technology.
 
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