Bullet Rise Due to Rifling

[NavyLCDR]

But the mind is the second thing to go!

Good thing I forgot what the first thing was....

 

[misANTHrope]

Bullets are the same shape all around, there is no way for them to create lift... the bullet would have to be wing shaped; something that is round or the same shape on all side won't create lift. If it created lift on the bottom, it would create "lift" on the top, canceling it out.

Slight correction... you don't need any kind of special shape to create lift. Lots of aircraft have symmetrical wings. For that matter, one could create lift using a brick, given sufficient airflow and angle of attack. But it would be damned inefficient.

In any case, thanks to gyroscopic stabilization of modern bullets, there is never going to be any appreciable angle of attack, and even if there were, the amount of lift would be negligible.

 

[deadin]

This is entirely dependent upon the range you are sighting at. In most handguns, the sight angle is set so the barrel is DOWNWARD, not up, at the moment of firing. This is because recoil pulls the firearm upwards. The longer the barrel, the more the firearm is displaced upward vs the aiming point, and the more you have to depress the sight angle to compensate for it.

This is true, but comes under the heading of "Interior Ballistics". Once the bullet leaves the barrel it is ruled by "Exterior Ballistics" and, as stated, does nothing but fall and possibly, drift.
I suppose there could be a case made that if the barrel were moving upward at the time of the bullet exiting, there could be a small amount of momentum imparted to the bullet that would carry it on upward until overcome by friction and gravity, but actually "flying" and gaining altitude, no.

 

[Kind of Blued]

What's their argument in the first place? Did you explain why that doesn't make sense? That should be pretty easy.

 

[Killermonkey21]

Their premise is the shape of the bullet (boat tail in their example) creates lift, thats why you see the arc in a tracer.

I tried to explain the difference in bore angle and sight angle yesterday, but one was arguing that:
-The bullet keeps accelerating for a while after it leaves the barrel (despite the gas not affecting it any more *rolls eyes*)
-And it creates lift through that acceleration

They kept trying to convince me that "watch the youtube videos of snipers, you can see the arc"
and I would respond: Thats because the bore angle is over the target, to account for bullet drop.
But at this point, one of them (PFC) has said "whatever, youre wrong, and I don't give a f***"
and the other SPC just said "w/e"

In regards to arguing with an E6. He interrupted the conversation with me and the SPC and PFC and tried to agree with them. I tried to use newtonian physics, but that didn't help, and my understanding of aerodynamics was very little (thank you for the diagrams) so he basically said "You have three people telling you you're wrong, so just show us and we'll believe you"
At this point I'm about to say "screw it" and let them be ignorant. Sometimes being right isn't worth the trouble.

 

[expvideo]

In regards to arguing with an E6....I tried to use newtonian physics...

ROFL. Found your problem.

 

[rcmodel]

At this point I'm about to say "screw it" and let them be ignorant.

Probably the best plan.

If you educate them to much, they will just become 2nd. Lieutenants.

And we already know you can't argue with them.

rc

 

[jakemccoy]

You think this argument is hard? Try arguing thermodynamics with somebody. I was recently on a site where 3 people were basically trying to tell me perpetual motion machines exist in some everyday appliances. One guy went so far as to scan his HVAC license. Well, then sign me up, trillionaire.

 

[misANTHrope]

At this point I'm about to say "screw it" and let them be ignorant. Sometimes being right isn't worth the trouble.

Probably a good plan. Sometimes being right isn't worth the blood pressure spike.

 

[jwr747]

so in a right hand twist barrel ,bullets rise and in a left hand twist they take a dive. sounds good to me. jwr

 

[Wheeler44]

so in a right hand twist barrel ,bullets rise and in a left hand twist they take a dive. sounds good to me

And they really fly through a 1:7" twist barrel....

If only we could fire a tracer through a musket (no rifling) we could show them some real flight..

 

[Dr. Tad Hussein Winslow]

A bullet can indeed rise or fall a bit due to the SPIN of the bullet (which is *imparted by* the rifling), just as a pitcher can curve a baseball up, down, left, or right. Most rifling is RH twist, meaning the bullet spins to the right. My understanding is that wind speed and direction makes the difference in whether the bullet lifts or drops. If the wind is from the left (with RH twist/spin), I believe the bullet will rise, but from the right, it will drop. Or it might be vice versa. But the wind plays a role.

All the above ignores the non-wind, non-lift induced flight path / bullet trajectory, which I believe is not the point of the thread.

 

[Cyborg]

Bullet vs Watch Question

I never took the Nuke test but did score 1 question short of perfect on both the Navy Officer and Pilot selection tests. But on the watch vs bullet question, depending on the barrel angle, in a vacuum (so no atmospheric drag issues) the watch should hit first. Here's why.

If you set as one of your starting conditions that the barrel is perfectly tangental to the earth's surface (cannot be parallell when one line is curved) then in effect the gun barrel is at the top of a semicircular hill. Assuming a perfectly spherical earth of diameter 8k miles and a bullet travel of 1000 feet, the bullet has an extra 8.65 X 10^-5 inches to fall. Admittedly it would take the atomic clock to measure the difference in time of fall but the watch would hit first since the earth is constantly curving away from it (at least theoretically).