To get it out of the other thread...
Originally Posted By: Shannow
There's a thing with wind drift in that it is proportional to the difference in vacuum time of flight versus actual (delay time), rather than actual time of flight.
It means that around the transonic range, there is a step change in how much longer a bullet takes to reach it's destination than the time that it takes to get there.
A .22 standard versus a super, the super takes a hit in wind drift...the magnum doesn't get it back, and IIRC, a hornet is still hanging out there.
For mental picture, consider two trains on parallel tracks. Distance between them in a vacuum takes the bullet "T" seconds", in air, it takes "T+t", t beign the delay.
Scenario 1 Target is stationary, rifle is on moving train, and trigger is pulled at target dead centre. The bullet is travelling in two planes, and losing velocity equally in both planes...it hits a distance away from the target. Whether it is a vacuum, or in air, the trajectory is the same, so the displacement is proportional to T.
Scenario 2 Target is moving, rifle is stationary, and trigger is pulled at target dead centre. It is still travelling a straight line, but takes T+t to get there...target has moved on for T+t seconds, so the movement of point of impact is T+t.
Scenario 3, target and rifle are on opposite tracks, moving with each other. Therefore the bullet already has the velocity of it's own train in that direction, and the sight/target are motionless compared to each other. Pull the trigger, and the bullet is slowing in two planes, and the displacement on target is proportional to the "t" component...not the time of flight.
Scenario 4...real life, the target and the rifle aren't on trains, and there's a wind blowing across between them. The reverse of 3 is observed, and the miss is proportional to "t", the delay time, as opposed to "T" the vacuum time, or "T+t" the actual time.
bullets that cross the sonic zone with variable loading are the worst at demonstrating this...and IMO, the .22 Mag is worse still.
Originally Posted By: Shannow
Wind drift is always related to the delay time (delta time of flight vacuum versus air), regrdless of velocity and time of flight.
Two bullets, same weight, same speed, different ballistic co-efficient, the one with the better ballistic co-efficient has less drift...not proportional to the time of flight, but due to the better performance of the good BC in air versus the other one.
http://www.dtic.mil/get-tr-doc/pdf?AD=ADA570469
Quote:
Abstract: This paper describes the internal, external, and terminal ballisticsof the 30-06 rifle cartridge.With cartridge case capacity of 68-70 grains of water and operating pressures up to 60,000 psi, the 30-06 launches 110-220 grain bullets with muzzle velocities between 3400 fps and 2400 fps, respectively. Low-drag bullets are available which make the 30-06 an effective and capable choice for target and anti-personnel use out to 1000 yards, but longer range applications are challenging due to the sonic transition. With an appropriate bullet choice, the 30-06 penetrates a variety of commonly encountered barriers. It also penetrates soft body armors and can deliver significant wounding effects even when stopped by hard body armor. At shorter ranges, wounding effects in human and deer-sized living targets are impressive and yield rapid incapacitation.
Quote:
Most ballistic calculators compute horizontal winddriftusing a procedure equivalent to the formula Wd = 17.6 x Vw x Tlag where Wd is the horizontal wind deflection (in inches), Vw is the cross wind velocity (in miles per hour), and Tlag is the lag time, or time delay between the time the bullet would reach that range in a vacuum and the time it actually takes when aerodynamic drag is included (in seconds).
It's counter-intuitive, but fact...you have to get the velocity and BC high enough to get the Tlag down to the same as a subsonic round to come back to the same drift.
It's just that in the world of trans-sonic bullets, the "delay" time is more for the supersoninc bullets out to a reasonable speed beyond sonic.
Originally Posted By: Shannow
There's a thing with wind drift in that it is proportional to the difference in vacuum time of flight versus actual (delay time), rather than actual time of flight.
It means that around the transonic range, there is a step change in how much longer a bullet takes to reach it's destination than the time that it takes to get there.
A .22 standard versus a super, the super takes a hit in wind drift...the magnum doesn't get it back, and IIRC, a hornet is still hanging out there.
For mental picture, consider two trains on parallel tracks. Distance between them in a vacuum takes the bullet "T" seconds", in air, it takes "T+t", t beign the delay.
Scenario 1 Target is stationary, rifle is on moving train, and trigger is pulled at target dead centre. The bullet is travelling in two planes, and losing velocity equally in both planes...it hits a distance away from the target. Whether it is a vacuum, or in air, the trajectory is the same, so the displacement is proportional to T.
Scenario 2 Target is moving, rifle is stationary, and trigger is pulled at target dead centre. It is still travelling a straight line, but takes T+t to get there...target has moved on for T+t seconds, so the movement of point of impact is T+t.
Scenario 3, target and rifle are on opposite tracks, moving with each other. Therefore the bullet already has the velocity of it's own train in that direction, and the sight/target are motionless compared to each other. Pull the trigger, and the bullet is slowing in two planes, and the displacement on target is proportional to the "t" component...not the time of flight.
Scenario 4...real life, the target and the rifle aren't on trains, and there's a wind blowing across between them. The reverse of 3 is observed, and the miss is proportional to "t", the delay time, as opposed to "T" the vacuum time, or "T+t" the actual time.
bullets that cross the sonic zone with variable loading are the worst at demonstrating this...and IMO, the .22 Mag is worse still.
Originally Posted By: Shannow
Wind drift is always related to the delay time (delta time of flight vacuum versus air), regrdless of velocity and time of flight.
Two bullets, same weight, same speed, different ballistic co-efficient, the one with the better ballistic co-efficient has less drift...not proportional to the time of flight, but due to the better performance of the good BC in air versus the other one.
http://www.dtic.mil/get-tr-doc/pdf?AD=ADA570469
Quote:
Abstract: This paper describes the internal, external, and terminal ballisticsof the 30-06 rifle cartridge.With cartridge case capacity of 68-70 grains of water and operating pressures up to 60,000 psi, the 30-06 launches 110-220 grain bullets with muzzle velocities between 3400 fps and 2400 fps, respectively. Low-drag bullets are available which make the 30-06 an effective and capable choice for target and anti-personnel use out to 1000 yards, but longer range applications are challenging due to the sonic transition. With an appropriate bullet choice, the 30-06 penetrates a variety of commonly encountered barriers. It also penetrates soft body armors and can deliver significant wounding effects even when stopped by hard body armor. At shorter ranges, wounding effects in human and deer-sized living targets are impressive and yield rapid incapacitation.
Quote:
Most ballistic calculators compute horizontal winddriftusing a procedure equivalent to the formula Wd = 17.6 x Vw x Tlag where Wd is the horizontal wind deflection (in inches), Vw is the cross wind velocity (in miles per hour), and Tlag is the lag time, or time delay between the time the bullet would reach that range in a vacuum and the time it actually takes when aerodynamic drag is included (in seconds).
It's counter-intuitive, but fact...you have to get the velocity and BC high enough to get the Tlag down to the same as a subsonic round to come back to the same drift.
It's just that in the world of trans-sonic bullets, the "delay" time is more for the supersoninc bullets out to a reasonable speed beyond sonic.
