Bullet trajectory
- Thread starter blackops
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Tarvis
Member
If you point the rifle at the sky and fire it, is it not true that the bullet is in fact rising? After all, the OP did ask if the bullet rises before it drops; in any instance where the muzzle is pointed "above level with the ground" (or however you are supposed to phrase that), yes, the bullet does rise before it drops. The idea that a bullet momentarily creates lift or temporarily defies the laws of physics... you get the idea.
What if someone created a bullet that would turn sideways after leaving the muzzle, causing the rifling grooves to create lift like a baseball? Then it really would rise... someone start designing a tiny gyroscope!
You meant to say because the rifling circles the bore, right? And what about wad cutters? Or are you trying to say that rifling is used so spitzers can be used? Sorry, I don't mean to pick on you or anything; it seems like you were making the point that rifling was invented for use with spitzer bullets.
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bigalexe
Member
I believe the formula for Bullet RPM is the following:
FPS*12*60*Twist=RPM
A breakdown is as follows:
FPS*12 gives you Inches Per Second, then Multiplied by 60 is Inches Per Minute. The Twist of a rifle is usually stated as follows 1/7 so thats 1 twist in 7 inches. Now what we needed to do was divide the inches of travel by the distance it takes a bullet to do a full rotation. Whats handy is that multiplying by a fraction is actually a division problem, so multiplying your inches per minute value by the fraction 1/7 actually divides by seven. So the result is you answer.
For more fun take your bullet diameter (ever so handy its the caliber) and multiply by Pi (3.14) and then multiply that value by your RPM. That would tell you how far sideways your bullet would travel if it were rolling on a surface instead of flying straight. This serves no purpose but: Its fun to find out that a .50 caliber bullet at 2000 FPS out of a 1/7 twist barrel would travel nearly 5 miles sideways in a minute.
FPS*12*60*Twist=RPM
A breakdown is as follows:
FPS*12 gives you Inches Per Second, then Multiplied by 60 is Inches Per Minute. The Twist of a rifle is usually stated as follows 1/7 so thats 1 twist in 7 inches. Now what we needed to do was divide the inches of travel by the distance it takes a bullet to do a full rotation. Whats handy is that multiplying by a fraction is actually a division problem, so multiplying your inches per minute value by the fraction 1/7 actually divides by seven. So the result is you answer.
For more fun take your bullet diameter (ever so handy its the caliber) and multiply by Pi (3.14) and then multiply that value by your RPM. That would tell you how far sideways your bullet would travel if it were rolling on a surface instead of flying straight. This serves no purpose but: Its fun to find out that a .50 caliber bullet at 2000 FPS out of a 1/7 twist barrel would travel nearly 5 miles sideways in a minute.
Black Ops: "I love how people take time to make a post and say something that everybody understands, but there is always one guy who wants to pick out the smallest imperfection as far as grammar or reasoning and act is if they are perfect."
I know what you mean. I guess gravity is acting on the bullet at all times, not just after leaving the barrel. It becomes about the semantics.
I know what you mean. I guess gravity is acting on the bullet at all times, not just after leaving the barrel. It becomes about the semantics.
content
Member
Hello friends and neighbors // Will rotating the position of the front sight from 12:00 to say 9:00 affect trajectory?
It seems the rifling is used in conjunction with the sights for a straighter shot.
It seems the rifling is used in conjunction with the sights for a straighter shot.
benEzra
Moderator Emeritus
Well, it could generate a teeny bit of lift it it were traveling sideways or at a significant yaw angle, but not while traveling point first to the relative wind (which it does to a tiny fraction of a degree).
BTW, to the OP's question, think of throwing a baseball 75 feet. The ball does not start out moving level to the ground and then rise after leaving your hand. You have to throw it at a significant upward angle to lob it any distance at all, and it never climbs above that initial trajectory. It's exactly the same with a bullet fired from a gun.
AKElroy
Member
I hope this is not a hijack, but I have a related question. I have a nikon BDC on a .243. Ordinarily, I would sight this rifle 1.5" high @ 100, but with the BDC, I have a 100, 200, 300 & 400 mil-dot circles in the reticle. Should I zero dead on @ 100 with this scope?
Eaglecreekbrewer
Member
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This is one thing I still remember from hs physics.
Velocity has no effect on gravity.
Problem:
Rifle barrel is level
Ground is level
Bullet is dropped by hand at barrel level, at the exact instant a bullet exits the barrel at 3000fps. Which bullet will hit the ground first?
Answer: They will both hit at the same time, even though one will be at your feet and the other will be thousands of feet away. The force of gravity is equal on both bullets.
Velocity has no effect on gravity.
Problem:
Rifle barrel is level
Ground is level
Bullet is dropped by hand at barrel level, at the exact instant a bullet exits the barrel at 3000fps. Which bullet will hit the ground first?
Answer: They will both hit at the same time, even though one will be at your feet and the other will be thousands of feet away. The force of gravity is equal on both bullets.
Art Eatman
Moderator In Memoriam
AKElroy, that should work IF the mil dots correspond to the trajectory of your bullet. If they don't, you either have to memorize what they actually represent or ignore them--and sight in for the commonly-used 200-yard zero.
Mr_Pale_Horse
Member
Yawing and/or pitching of bullets - It happens, but the effects are not perceptible at ranges as short as a few hundred yards, for 2 reasons.
1. The bullet is hyper-sonic. Suffice it to say, airflow models at the surface of the bullet are not those witnessed in a physics class demonstration with a TP tube.
2. In real time, bullets cover alot of ground fast. 200,000 rpm sounds like alot, but a bullet can cover 100 yards in ~100 milliseconds, or .1 seconds, or 333 revolutions.
At 1000 yards, 168 grain bullet with a nominal .5 ballisctic coefficient, reaches that range in 1.461 seconds, at least according to the exterior ballistics program I have. Not nearly enough time for a pitch/yaw induced rise to be perceptible. Moreover, it is still supersonic at that range.
1. The bullet is hyper-sonic. Suffice it to say, airflow models at the surface of the bullet are not those witnessed in a physics class demonstration with a TP tube.
2. In real time, bullets cover alot of ground fast. 200,000 rpm sounds like alot, but a bullet can cover 100 yards in ~100 milliseconds, or .1 seconds, or 333 revolutions.
At 1000 yards, 168 grain bullet with a nominal .5 ballisctic coefficient, reaches that range in 1.461 seconds, at least according to the exterior ballistics program I have. Not nearly enough time for a pitch/yaw induced rise to be perceptible. Moreover, it is still supersonic at that range.
Mr. Pale Horse sez:
It'll be supersonic at 1000 if it's a 30 caliber one leaves at least 2600 fps. The military M852 7.62 NATO match ammo with this bullet oft times didn't shoot fast enough from 22-inch barrels on M14's; they went subsonic at about 900 yards and accuracy suffered.
There are two kinds of knowledge. Head kind and experiece kind. When the two are melded together and refined (ie the crap is thrown out of the equation) then you have rc's knowledge. Thinking and believing something to be true is not the same as doing it.
AKElroy
Member
Thanks Art. I cannot break years of practice, so I will be sighting for a 200 yrd zero & ignoring the mil-dots. Should have saved $10.00 on the scope & gone with the standard reticle.
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