A Dumb Question About Trajectory

[the old grind]

No bullet is ever fired perfectly horizontal (or parallel to line of sight) if gun and target are at the same altitude.


Many don't realize that a bullet/pellet crosses LOS twice. Those that do often sight in so that the high point of trajectory brackets them into a range of distance to be fired at 'point blank' by holding the cross-hairs 'dead on'. The arc of trajectory determines those bracket points and the high point (above LOS) represents roughly half of the 'target circle' a round should land in. The low point within that circle will be somewhat beyond the second crossover point (intersection).

With a typical CF hunting rifle (.30-06, .308, .270, etc) this takes a hundred yards or so. Sighting 2-3" high at 100yd will put one roughly dead-on at 200yd or so and within the target circle somewhat beyond that (say another 50yd). With a pellet gun this happens within feet vs yds but the principle is the same. Because of the LOS's height above the barrel extremely close shots require holding high to compensate for it (up to the first 'crossover point'.)

That a trajectory ever matches line of sight (dead-on) at all ranges is the domain of video games. To those who work out their sight-ins considering all possible shooting distances (feet or yards) much of this is old hat, whether the physics is fully understood or not. Others just ask, but I doubt that any experienced shooter would consider the OP's question a 'dumb' one.
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Wow! 4 posts since I started typing. (good info continues apace. )

 

[teejk]

Haven't seen any answer the second point of the question yet..."store bought" BB/pellet guns are indeed accurate (I have Daisy and Crossman). I set up a basement trap for the kids (guessing 30 ft or so) to introduce gun handling and safety. Not so sure it would kill anything but they can be "dialed in". I still use them to warn squirrels at the bird feeders.

 

[SPYDERLK]

I have always thought of it like this: The trajectory of a bullet sighted in at say 50 yards will have a trajectory like a rainbow (slight exaggeration). Depending on how the gun is sighted in, the bullet will be dead on the line of sight at say 50 yards and again about 100 yards. Because of the rainbow effect, caused by gravity and the fact that the aim is ever so slightly at an upward angle, the trajectory will place the bullet below the aiming point at a distance below 50 yards, above the aiming point beyond 50 but less than 100; right on at 100 and below beyond 100.

If you are shooting straight up or straight down, the effect of gravity on the trajectory is minimal, ergo the bullet will be high at the point of aim (since there is no compensation for gravity), therefore aim a little low...

No bullet is ever fired perfectly horizontal (or parallel to line of sight) if gun and target are at the same altitude.
View attachment 446855

Many don't realize that a bullet/pellet crosses LOS twice. Those that do often sight in so that the high point of trajectory brackets them into a range of distance to be fired at 'point blank' by holding the cross-hairs 'dead on'. The arc of trajectory determines those bracket points and the high point (above LOS) represents roughly half of the 'target circle' a round should land in. The low point within that circle will be somewhat beyond the second crossover point (intersection).

With a typical CF hunting rifle (.30-06, .308, .270, etc) this takes a hundred yards or so. Sighting 2-3" high at 100yd will put one roughly dead-on at 200yd or so and within the target circle somewhat beyond that (say another 50yd). With a pellet gun this happens within feet vs yds but the principle is the same. Because of the LOS's height above the barrel extremely close shots require holding high to compensate for it (up to the first 'crossover point'.)

That a trajectory ever matches line of sight (dead-on) at all ranges is the domain of video games. To those who work out their sight-ins considering all possible shooting distances (feet or yards) much of this is old hat, whether the physics is fully understood or not. Others just ask, but I doubt that any experienced shooter would consider the OP's question a 'dumb' one.
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Wow! 4 posts since I started typing. (good info continues apace. )

Yes. ... Left unsaid, but clear in the graphic, it is the bores offset below the sight that influences the angle where sight and trajectory cross. - This makes a guns characteristic different with regular vs telescopic sights since the telescope sets higher above the barrel.

With standard sight a 30-06 set dead on at 30 yds shoots real good out to about 300. ... AIR, it goes about 2" high at ~100yds and about 4" low at 300.

With scope, higher above the barrel, the 30yd sight in will require a more acute upward correction. Thus the bullet will rise higher above the sight line before beginning to drop.

 

[Streetcar]

Haven't seen any answer the second point of the question yet..."store bought" BB/pellet guns are indeed accurate (I have Daisy and Crossman). I set up a basement trap for the kids (guessing 30 ft or so) to introduce gun handling and safety. Not so sure it would kill anything but they can be "dialed in". I still use them to warn squirrels at the bird feeders.

The pellets that I have used have imperfections. I think the imperfections have more influence than gravity

 

[fordmantpw]

If you want to play with different effects on trajectories, bullet types, etc., check out the ballistics calculator from Winchester. It's pretty cool: Winchester Ballistics Calculator

A few of my co-workers developed it for Winchester. I'm a bit bummed I didn't get to work on that project.

 

[teejk]

If you want to play with different effects on trajectories, bullet types, etc., check out the ballistics calculator from Winchester. It's pretty cool: Winchester Ballistics Calculator

A few of my co-workers developed it for Winchester. I'm a bit bummed I didn't get to work on that project.

I used it a lot (I get really nervous about how far my bullets travel when target shooting plus it's nice to know how much +/- I need on a particular load when shooting a deer outside my 100 yd sight-in range) but can't get it work since Win10/Edge. It requires MS SilverStream (or something like that) and it apparently doesn't work (an MS problem, not Winchester).

 

[/pine]

...Thus the bullet will rise higher above the sight line before beginning to drop...

On a technical point...not trying to be **** about it.

The laws of physics state that the bullet starts to drop the instant it leaves the muzzle...aerodynamics of a spinning projectile (not velocity) resists the force...fired in 0 atmosphere (total vacuum) a bullet would not rise...

Air density and pressure are key factors in sniper training...

 

[fordmantpw]

I used it a lot (I get really nervous about how far my bullets travel when target shooting plus it's nice to know how much +/- I need on a particular load when shooting a deer outside my 100 yd sight-in range) but can't get it work since Win10/Edge. It requires MS SilverStream (or something like that) and it apparently doesn't work (an MS problem, not Winchester).

If you want to run it, you can run it under Internet Explorer on Win 10. Just hold down your window key and hit 'R'. Then type 'iexplore' and it will open up the old Internet Explorer. Then you can install Silverlight and run the app. Edge does not allow the plugins. You can also run it under Chrome if you want.

 

[EarPlug]

I used it a lot (I get really nervous about how far my bullets travel when target shooting plus it's nice to know how much +/- I need on a particular load when shooting a deer outside my 100 yd sight-in range) but can't get it work since Win10/Edge. It requires MS SilverStream (or something like that) and it apparently doesn't work (an MS problem, not Winchester).

Microsoft Explorer (or Chrome) can be used on a Win 10 computer. Explorer does support MS Silverlight.

 

[fordmantpw]

Microsoft Explorer (or Chrome) can be used on a Win 10 computer. Explorer does support MS Silverlight.

Internet Explorer does, Edge does not.