PDA

View Full Version : Gyroscopic drift (Spin drift) and Bullet Rise?


R.Miksits
08-17-10, 16:58
Hey doc,

does Gyroscopic drift (Spin drift) cause the bullet to rise at any point during its flight? if so how to calculate it?

If the bullet does not rise, does Gyroscopic drift (Spin drift) from the bullet have any affect on the altitude of the projectile?

I am aware that Gyroscopic drift (Spin drift) has a left or right affect depending on twist direction.

Also we are assuming the barrel is parallel (not perpendicular as said before edit) to the ground. Taking the POA and POI out of the equation.

thanks doc.
TiroFijo
08-17-10, 18:31
Did you mean barrel parallel to the ground, like horizontal shooting?

Gyroscopic drift never lifts the bullet, it is always falling... the yaw of repose for a RH barrel is with the nose up and to the right, so it does have a very minor effect on drop at extended (> 800 m for normal rifle calibers) distances, but I don't know how to calculate it. Normal ballistic programs do not account for it, you would need extensive doppler radar data and 6 DOF calculations. Lapua has released their radar data to the public (only manufacturer that I'm aware of), at least for some long range bullets, so you could write to them to try to get a quantitative answer.

Contrary to the common myth (mythbusters included) the drop of a fast moving bullet is not the same as one bullet that is simply dropped, in the same time lapse, because the vertical component of the air drag is quite significant.
randolph
08-17-10, 18:50
this is basic Ballistics 101.
bullets never rise after it leaves the barrel, its not self propelled, its being pushed, therefor it begans to slow down and fall instantly.

someone will come along and give you a technical answer soon :p
R.Miksits
08-17-10, 20:57
for the purpose of my question. the barrel is parallel to the ground. No looking through a sight of any kind. Taking the line of sight out of question and zero's.

Will Gyroscopic drift (Spin drift) cause any rise in projectile at all.
NMBigfoot02
08-18-10, 16:08
for the purpose of my question. the barrel is parallel to the ground. No looking through a sight of any kind. Taking the line of sight out of question and zero's.

Will Gyroscopic drift (Spin drift) cause any rise in projectile at all.

I'm not Doc, but the answer is no. The bullet begins falling immediately after leaving the barrel. Any "rise" that is quoted in ballistics tables is relative to the sights, not the ground.
markm
08-18-10, 18:33
Spin drift will slightly pull your POI up and to the right or left. You're not gaining altitude so to speak. But when you get out to the outer limits of 7.62, for example, you may notice a POI shift up and to one side.

IMO, you really have to be reaching out there before spin drift is a factor.