Thread: rounds going "up" out of the barrel

OK, just had a "discussion" with someone at work regarding the old chestnut of rounds rising before they start to fall again.

He accepted that this appeared to be the case due to the line of the scope intersecting the trajectory of the projectile, and that, given a projectile fired from a barrel aligned perpendicular to the force of gravity, the round would never rise above the point at which it exited the barrel, except fir the fact the the spin on the projectile gives it "lift"

I cant see it myself, but didnt argue the toss too hard due to being on uncertain ground ..

I think hes wrong.

Your 5 ten or 20 cents would be appreciated ...

Tim

The scope is never aligned perfectly with the barrel otherwise we would never hit what we are aiming at.
I don't believe they climb they just leave the barrel at an upward Trajectory RELATIVE to the scope line of sight. Where they intersect is up to you by adjustment.
Hence the reason for canted bases for long range shooting.

Not unless shooting across a gully with an updraft or thru cumulo-nimbus cloud

actually, just having read my initial post, I probably communicated incorrectly ..

the question is whether or not the projectile ever passes above a line projected directly along the axis of the bore .....

obviously gravity would be a force that cause the projectile to sink below that line, so any lifting above this line (for example due to spin) would require a force greater than that of the gravity acting on the projectile

Tim

Yep, they definarety climb but its due to the angle they are fired ie slightly up so that it rises above line of sight and then drops back below it, what he is saying would be like saying when you throw a ball it never rises above the height of your hand!

Ah, i see what you are getting at, no, technically it should never rise above the bore line, it may leave the bore at a slightly off angle due to a messed up crown or something like that, i don't believe spin drift would ever cause it to climb but rather slow its descent slightly as the force is less than that of gravity.

Google some trajectory diagrams, they are probably the best way to get your head around it.

yeah I got my head around the fact that the axis of the scope's crosshair intersects the projectiles trajectory some time ago.

its just this question of "lift" due to spin.

Not sure on that one Tim. Unless projectiles are influenced by gyroscopic precession (They are not I am sure) as they leave the bore I cannot see how they lift above the axis. A badly cut crown in theory could/will do it. Not 100% sure tho. Some physics legend may say otherwise.

Originally Posted by R93

Not sure on that one Tim. Unless projectiles are influenced by gyroscopic precession (They are not I am sure) as they leave the bore I cannot see how they lift above the axis. A badly cut crown in theory could/will do it. Not 100% sure tho. Some physics legend may say otherwise.

Where is Gimp when you need him! Sure he will put us straight!

My gut feel is that precession being what it is and, remembering my 100+ hours in a cub and 200 odd in a pawnee , precession would more likely swing the projectile left or right - not up or down ...

"bring out the gimp"

I'm sure someone can dig up some Litz - although I can't find anything online

How does it know which way is wich when leaving a tube? Your not thinking of phase lag? There is a slight possibility I am confusing the shit out of my self now.
Im gunna go back to staring at this cool spot on the wall.

Is it climbing if sighted in at 100 and you re shooting at a deer 10 feet away.
Couple weekends ago my hunting mate shot twice at real close range and I saw both go over the top.
The gun was on target , sighted in two days previous and accurate.
He got to grips with it on his last shot and got one but was struggling. Next day 100 mtrs bang one shot in the heart .
Is this what your mate is referring too ?

What you are talking about is the Magnus effect for that "lift". In short no the bullet will not lift due to this force. As the bullet is spinning perpendicularly to it's advance all forces are balanced. When a ball spins (back spin) and gets lift this is because it helps the air above move faster (low pressure) and slows the air below it down ( high pressure).


But as I said the bullet is spinning perpendicularly to the on coming wind so will not observe this effect. If there is a strong side wind though this will make the bullet rise/drop dependent on wind direction and spin (left/right) of the barrel.

I believe a cross wind does account for a very small amount of lift or drop (depending on direction) and ballistic programmes account for this but certainly not enough to overcome gravity!

I believe that if you first dip the projectile in some "Red Bull", there would be some significant lift.