I always thought that a bullet starts dropping right when it exits the barrel. However most ballistics data I see indicates that the bullet actually rises. For instance an AR-15 with the 25 yard zero is supposed to be dead on at 300 yards since the bullet rises and peaks somewhere in between and then drops back down to the same level at 300. What causes the bullet to rise?
Why do bullets rise?
- Thread starter chasep255
- Start date
You are correct when you state that bullets start dropping as soon as they leave the barrel. Since I can't draw a picture here, try to picture a barrel canted upward with your line of sight through the sights being a straight line. A straight line from the barrel will cross this other line from the sights twice, which is where the 25/300 zero comes in. The bullet is dropping, but since the barrel is canted slightly upward, it is "climbing".
Hope that made sense without a picture.
Hope that made sense without a picture.
Drummer101
New member
They fly in a parabola.
Picture the bullet's path as a parabola or arc, that will cross your line of sight going up from below, then down from above. Picture, too, that the bullet's forward velocity is being constantly slowed by the drag of the air.
Your near zero will be hit when the bullet rises to meet the line of sight. (With an AR of M16 barrel length, that's normally set at 25m.) Your far zero will be when the bullet has dropped back down to line of sight. (With an AR of M16 barrel length, with initial zero at 25m, that's normally at 300m.) Between those distances, the bullet is flying an arc, climbing above the line of sight, then dropping back to it. Past the far zero, the bullet starts dropping more rapidly, as it accelerates downward with gravity, and as its forward velocity is slowed by aerodynamic drag.
The faster the bullet, the flatter the arc. The slower the bullet, the more a "garden hose" type trajectory is required at distance.
Your near zero will be hit when the bullet rises to meet the line of sight. (With an AR of M16 barrel length, that's normally set at 25m.) Your far zero will be when the bullet has dropped back down to line of sight. (With an AR of M16 barrel length, with initial zero at 25m, that's normally at 300m.) Between those distances, the bullet is flying an arc, climbing above the line of sight, then dropping back to it. Past the far zero, the bullet starts dropping more rapidly, as it accelerates downward with gravity, and as its forward velocity is slowed by aerodynamic drag.
The faster the bullet, the flatter the arc. The slower the bullet, the more a "garden hose" type trajectory is required at distance.
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charles-smythe
Inactive
the point of impact for a .22 long rifle is the same @ 25 & @ 100 yards...that means that if your .22 is zeroed in @ 25 yard the same sight picture will hit the X ring @ 100 yards......when I was younger (20 to 40) very few Texans realized this...since Texans will put their money where their month is my Highstandard citatian supermatic with adj sights and 5 1/2 inch bull barrel won me a lot of money...lol...
Here's a pretty neat article with pictures explaining it...
http://forum.pafoa.org/general-2/37393-arc-bullet.html
http://forum.pafoa.org/general-2/37393-arc-bullet.html
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Good thread...
I, too, used to think that bullets flew in an arc from a horizontal barrel...
The term "flat-shooting" gets thrown around alot, especially in the LR target game.
But after doing a little reading about external ballistics, it appears not to be the case. The "rise" of the bullet is due to the sighting plane as mentioned above- depends on where your rifle sights, or scope, is zeroed. As kraigwy simply stated, the barrel is pointed up. The parabolic flight of the bullet is due to the angle of the bore.
Due to the near parabolic shape of the projectile path, the line of sight or horizontal sighting plane will cross the projectiles trajectory at two points called the near zero and far zero in case the projectile starts its trajectory (slightly) inclined upward in relation to the sighting device horizontal plane, causing part of the bullet path to appear to rise above the horizontal sighting plane. The distance at which the firearm is zeroed, and the vertical distance between the sighting device axis and barrel bore axis, determine the apparent severity of the "rise" in both the X and Y axes (how far above the horizontal sighting plane the rise goes, and over what distance it lasts).
Many firearms ballistics tables and graphs show a rise in trajectory at distances shorter than the one (far zero) used for sight-in. This apparent "rise" of the projectile in the first part of its trajectory is relative only to the sighting plane, and is not actually a rise. The laws of physics dictate that the projectile will begin to be pulled down by gravity as soon as it leaves the support of the barrel bore at the muzzle, and can never rise above the axis of the bore. The apparent "rise" is caused by the separation of the plane of the sighting device axis and that of the bore axis and the fact that the projectile rarely leaves the bore perfectly horizontally. If a firearm is zeroed at 100 meters, then the far horizontal sighting plane and the projectile path must "cross" at that distance; the sighting line must be adjusted to intersect with the projectile path at 100 meters. In the case of a bore axis that is maintained in a perfectly horizontal position, the sighting device must be inclined downward to achieve this intersection. The axial separation distance between the line of sight and the bore axis and trajectory of the projectile dictate the amount of angular declination required to achieve the required intersection.
I, too, used to think that bullets flew in an arc from a horizontal barrel...
The term "flat-shooting" gets thrown around alot, especially in the LR target game.
But after doing a little reading about external ballistics, it appears not to be the case. The "rise" of the bullet is due to the sighting plane as mentioned above- depends on where your rifle sights, or scope, is zeroed. As kraigwy simply stated, the barrel is pointed up. The parabolic flight of the bullet is due to the angle of the bore.
Due to the near parabolic shape of the projectile path, the line of sight or horizontal sighting plane will cross the projectiles trajectory at two points called the near zero and far zero in case the projectile starts its trajectory (slightly) inclined upward in relation to the sighting device horizontal plane, causing part of the bullet path to appear to rise above the horizontal sighting plane. The distance at which the firearm is zeroed, and the vertical distance between the sighting device axis and barrel bore axis, determine the apparent severity of the "rise" in both the X and Y axes (how far above the horizontal sighting plane the rise goes, and over what distance it lasts).
Many firearms ballistics tables and graphs show a rise in trajectory at distances shorter than the one (far zero) used for sight-in. This apparent "rise" of the projectile in the first part of its trajectory is relative only to the sighting plane, and is not actually a rise. The laws of physics dictate that the projectile will begin to be pulled down by gravity as soon as it leaves the support of the barrel bore at the muzzle, and can never rise above the axis of the bore. The apparent "rise" is caused by the separation of the plane of the sighting device axis and that of the bore axis and the fact that the projectile rarely leaves the bore perfectly horizontally. If a firearm is zeroed at 100 meters, then the far horizontal sighting plane and the projectile path must "cross" at that distance; the sighting line must be adjusted to intersect with the projectile path at 100 meters. In the case of a bore axis that is maintained in a perfectly horizontal position, the sighting device must be inclined downward to achieve this intersection. The axial separation distance between the line of sight and the bore axis and trajectory of the projectile dictate the amount of angular declination required to achieve the required intersection.
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There are a few things wrong with this post. Not every rifle or handgun has the sights the same height above the bore, different ammo is loaded to different velocities, different bullets have different ballistic coefficients, and even if everything else was the same you still have to account for differences in barrel length as well as the fact that not all barrels perform the same anyways. I can assure you that my 22's, which are zeroed at 25 yards are not zeroed at 100.
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Back in the "good old days" nobody knew about parabola or sight height or ballistic coeffecients so none of the stuff we know today applied. They did fabulous and sometimes unbelievable things with firearms then.
And of course since everything is bigger in Texas. The targets were bigger and the bullets were bigger. And there was only one brand of 22 (and believe it or not even they were bigger) available at the blacksmith and general store, so everyone knew exactly where those bullets would fly. So it is entirely possible that the POI at 25 and 100 would be at the same POA, because thats the way it was in that magical time and place. Ranges in those days were always aligned with the prevailing wind, which could have helped a bit.
o
And of course since everything is bigger in Texas. The targets were bigger and the bullets were bigger. And there was only one brand of 22 (and believe it or not even they were bigger) available at the blacksmith and general store, so everyone knew exactly where those bullets would fly. So it is entirely possible that the POI at 25 and 100 would be at the same POA, because thats the way it was in that magical time and place. Ranges in those days were always aligned with the prevailing wind, which could have helped a bit.
o
Art Eatman
Staff in Memoriam
Funny. I figured out trajectory with my Daisy Red Ryder. 1942. Austin, Texas. My grandfather taught me about it. He'd learned in, oh, maybe 1890, long before he got his Master's in Physics.
charles-smythe, you likely were winning money from immigrants from Massachusetts...
charles-smythe, you likely were winning money from immigrants from Massachusetts...
Because you just put fire to their little rear ends so they unfurl their tiny wings and try to fly up up and away. However they get tired easily and soon fall to the ground.
My bullets go up because I point the barrel up to compensate for the fact that gravity is going to be pulling my bullet down just as soon as it leaves the muzzle of my gun. Sight height does make a difference. Especially if you are using a scope and the sight line is higher off the line of the barrel than your iron sighted gun. With my (2) 10/22's, one scoped, one iron sighted with aperture sights the difference is 2" vs 4 1/2" between 25 yards and 100 yards. Seems counter-intuitive but that's the way it works out.
According to my ballistics chart, a 52 grain .233 bullet with a muzzle velocity of 3700 fps mounts on a barrel with a scope 1.25 above the barrel center and zeroed at 25 yards will also be zeroed at 300 yards. So ChaseP255, you are right on with your assumption but it only works for certain speeds and bullet weights and scope mounts. You have to recalculate for every variation.
Sorry to report Charles-Smythe - that I could find no combination that works for a 22LR, zeroed at 25 yards that could possibly also be zeroed at 100 yards. It may hit a 5 inch x-ring but it isn't the same zero point.
For a 1400 fps 32 grain 22LR bullet mounted on a barrel with a scope 1.25 inches above the barrel and zeroed at 25 yards would be 0.02 inches low at 50 yards and 4.83 inches low at 100 yards.
For a 1100 fps 40 grain 22LR bullet mounted the same way and zeroed at 25 yards would be 8.73 inches low at 100 yards.
By the way, using a 10 yard zero, a .22 LR 1400 fps bullet with the same scope mount could be just 0.29 inches off dead zero at 100 yards.
By the way, the 25 yard - 100 yard zero works within 0.04 inches for 2000 fps muzzle velocity and 175 gr .308 bullet with a ballistics coefficient of around .260 (I guess that would be an enemic .30-30 load).
Sorry to report Charles-Smythe - that I could find no combination that works for a 22LR, zeroed at 25 yards that could possibly also be zeroed at 100 yards. It may hit a 5 inch x-ring but it isn't the same zero point.
For a 1400 fps 32 grain 22LR bullet mounted on a barrel with a scope 1.25 inches above the barrel and zeroed at 25 yards would be 0.02 inches low at 50 yards and 4.83 inches low at 100 yards.
For a 1100 fps 40 grain 22LR bullet mounted the same way and zeroed at 25 yards would be 8.73 inches low at 100 yards.
By the way, using a 10 yard zero, a .22 LR 1400 fps bullet with the same scope mount could be just 0.29 inches off dead zero at 100 yards.
By the way, the 25 yard - 100 yard zero works within 0.04 inches for 2000 fps muzzle velocity and 175 gr .308 bullet with a ballistics coefficient of around .260 (I guess that would be an enemic .30-30 load).
Yep, with a 5.5 inch barrel the bullet would be much slower at the muzzle and would spend more time getting to the target and therefore the force of gravity would make it drop even further.
Both the bullets drop the same amount over time, but the one moving faster covers more distance so it appears to drop less when it covers the same amount of distance.
The problem with a .22 LR is the initial velocity. It is just too slow so it has to drop more over that same distance.
The reason that the .223 manages to zero at 25 and 300 yards is because it is flying so much faster (so it drops less over the distance even though it drops the same amount for equivalent time). Thus the expression shooting flatter is really shooting faster.
Both the bullets drop the same amount over time, but the one moving faster covers more distance so it appears to drop less when it covers the same amount of distance.
The problem with a .22 LR is the initial velocity. It is just too slow so it has to drop more over that same distance.
The reason that the .223 manages to zero at 25 and 300 yards is because it is flying so much faster (so it drops less over the distance even though it drops the same amount for equivalent time). Thus the expression shooting flatter is really shooting faster.
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Major Dave (retired)
New member
The barrel is NOT angled upward...
Actually, the SIGHTS are angled downward, to intersect the trajectory of the bullet, as it falls below the "line of bore". A bullet NEVER rises ABOVE the "line of bore". NEVER, Never, never!!!
Doesn't matter if the sights are "open iron", peep, or some kind of optic.
It's the responsibility of the shooter to "zero the sights"....., not "zero the barrel"!!
Actually, the SIGHTS are angled downward, to intersect the trajectory of the bullet, as it falls below the "line of bore". A bullet NEVER rises ABOVE the "line of bore". NEVER, Never, never!!!
Doesn't matter if the sights are "open iron", peep, or some kind of optic.
It's the responsibility of the shooter to "zero the sights"....., not "zero the barrel"!!