Boat tail vs flat base boolits

[popper]

Well, once in the barrel and once on the way to the target. General bullet design is to reduce air friction and turbulence that reduce velocity and interfere with gyro stability. The turbulence range (~speed of sound) is actually a 'range' of velocity that changes with atmospheric conditions.

[Lloyd Smale]

I thought mach 2 mach 3 ect were just a speed. Once a bullet breaks the sound barrier there is only one speed of sound and that's where the air disturbance is and it doesn't break it again and cause another sonic boom again when it goes twice the speed of sound. Either way its irrelevant in bullets because I don't know of a single one of them that does mach 2. Ive never heard of a plane or anything else that does it more then once unless you slow to slower then the speed of sound and accelerate through it again which no bullet can do. Going past the speed of sound Mach I causes a disturbance in the air and mach 2 mach 3 ect are just a speed based on the speed of sound

Lloyd

Bullets, airplanes, rockets and other projectiles can "break the sound barrier" (which is simply a term for speed)/velocity) several times. It's called MACH I, MACH II, MACH III, etc.

[Larry Gibson]

Lloyd

Yes, Mach I and Mach II are speeds but there is a shock wave that forms as the bullet/aircraft, etc. passes through Mach I. The shock wave changes in force, intensity and location created on the bullet/aircraft, etc. as additional Mach levels are passed. However you hear only one sonic boom, crack or whatever you call it when the shock wave reaches you. The shock wave follows behind and outwardly from the path of the bullet/aircraft, etc. You hear only one "boom/crack" regardless of whether additional Mach levels are reached later because the shock wave/boom is already past you. If it's going Mach I, II or III you will hear only one boom/crack because there is usually only one shock wave created regardless of the mach level or if more they are so close together you can't distinguish between them.

"Either way its irrelevant in bullets because I don't know of a single one of them that does mach 2."

Uh, Lloyd, lots of bullets travel faster than Mach II.......any over 2200 - 2400 fps are traveling Mach II or greater. You only hear one "crack" (if the muzzle blast is suppressed) because if the muzzle velocity is above Mach I, II or III it is already that Mach level speed on exit from the muzzle. There is no "crack" of the bullet while it is still inside the restriction of the barrel reaching whatever Mach level+ it exits the muzzle at.

Since the bullet is at max velocity on muzzle exit it will not increase in velocity and go "through" another Mach level (perhaps this is what you meant?).

[Ballistics in Scotland]

I don't understand how a bullet can break the sound barrier more then once.

Strictly speaking no bullet or aeroplane ever breaks through a barrier. of sound waves. What happens is that the velocity of sound in a medium varies with its density, being greater as the density of air increases. A tiny cushion of highly compressed air builds up in front of the bullet's nose, and in it the speed of sound increases, so that the bullet never quite catches up.




This picture, illuminated by the quite incredible brevity of an electric spark, was taken by a Professor Boys of Imperial College in the 1890s, and is much better that Dr. Mach was taking at the time. The shock-wave in uncompressed air, non-existent or very slight when the bullet is subsonic, becomes sharp and rather percussive on the eardrum. This is the sonic crack or boom. The nature of this wave structure explains some important facts.

The wave doesn't shoot out like growing whiskers. It travels at right angles to its front, so that the part of it behind the rear of the bullet was created in about the spot where the contact wire changes from thick to thin. As it is travelling in ordinary air, we could calculate bullet velocity from its angle, sharper as bullet velocity increases.

The rounding of the apex of the bow-wave is due to the compression of the air near the bullet. Greater roundness tells us that it was disturbing the air more. If the bullet was invisible, we could tell from the extent of that rounding how well shaped it was, to minimise disturbance of the air.

Like a seagull bobbing up and down as the waves of the sea pass under him, the air molecules oscillate but do not travel with the wave. (If you want to detect the first trace of an unhealthy noisez in your car engine, press a screwdriver against it and put your ear to the other end, as sound travels extremely well in the virtually immovable molecules of steel.) This is why only metal makes a clean hole in a target card, sometimes "pencilled" with lead, rather than the zone of elevated pressure.

As the wave can only travel at Mach 1, a bullet travelling at Mach 3 or more, with a more sharply angled bow-wave than Professor Boys's Lee-Metford bullet, can.t make the sound any greater. With a larger bullet, however, it does increase. A supersonic aircraft at close range can damage ears and break windows, but a bullet which doesn't hit them can't.

The bullet has hurled away a little cloud of pulverised contact wire, which (I think due to the elasticity of the metal) has acquired a higher velocity than the bullet that did it. This may be very important for wounding effect. General Hatcher tells of an experiment with a terminally sick mule, wearing a GI helmet. (It may have inspired the understandably worried one in the cartoon "The Old Western Scrounger" used to have in their catalogue.) Not only did a solid copper .220 Swift bullet penetrate it, but fragment of skull did on the way out.

Note that there is an extra wave originating at the rear of the bullet, and very slight ones from cannelures etc. So there is indeed a double sonic boom. I remember it well at a range of many miles, when they were testing the airliner Concorde in the North Channel between Scotland and Ireland. Due to its very great size, he sound carried very far. Being about 200 feet long, the booms should in theory have been around a sixth of a second apart. In fact they are both slightly drawn-out by distance, and sound more separate. But with a bullet, they can't be distinguished by the ear.

The same object can emit a sound fairly describable as a sonic crack or sonic crack, as the sound of a bullet is altered in pitch by the Doppler shift. The sound vibrations a the front are compressed by the movement of their source, and in a rearward direction stretched further apart. Think of a machine-gun in an aeroplane, and streams of bullet fired to front or rear. So the bullet passing close by you makes a vicious crack, as if it was carrying its own health warning, while from your own departing bullet the same sound may be heart as a low rumble.

The Doppler shift is why we hear a quick deepening of the bullet’s note as it passes, like a faster version of a passing car. Civil War veterans described the voice of a Minié bullet, from a direction range officers don't allow, as a chirp. A Union private at the all-American version of the battle of Yorktown observed a soldier named Spinney showing an unbecoming concern for his health. He afterwards explained that every bullet which passed said ‘Spinney’, which appeared just a little too personal for comfort.

[Lloyd Smale]

your right larry I don't know what I was thinking. I was mixing up a 1000fps with a 1000 mph.

Lloyd

Yes, Mach I and Mach II are speeds but there is a shock wave that forms as the bullet/aircraft, etc. passes through Mach I. The shock wave changes in force, intensity and location created on the bullet/aircraft, etc. as additional Mach levels are passed. However you hear only one sonic boom, crack or whatever you call it when the shock wave reaches you. The shock wave follows behind and outwardly from the path of the bullet/aircraft, etc. You hear only one "boom/crack" regardless of whether additional Mach levels are reached later because the shock wave/boom is already past you. If it's going Mach I, II or III you will hear only one boom/crack because there is usually only one shock wave created regardless of the mach level or if more they are so close together you can't distinguish between them.

"Either way its irrelevant in bullets because I don't know of a single one of them that does mach 2."

Uh, Lloyd, lots of bullets travel faster than Mach II.......any over 2200 - 2400 fps are traveling Mach II or greater. You only hear one "crack" (if the muzzle blast is suppressed) because if the muzzle velocity is above Mach I, II or III it is already that Mach level speed on exit from the muzzle. There is no "crack" of the bullet while it is still inside the restriction of the barrel reaching whatever Mach level+ it exits the muzzle at.

Since the bullet is at max velocity on muzzle exit it will not increase in velocity and go "through" another Mach level (perhaps this is what you meant?).