I am missing something fundamental, and hope one or more of you can fill in the missing piece(s). I was reading the urban disorder - sighting range thread and it's very clear that this relies on the ballistics curves. And they all start out with the projectiles rising, hitting a top point and then falling. OK, that makes sense.

But, somehow, I'm missing something. Here in Newton's universe (Einstein, just go away! ) everything from apples to anvils to moving bullets falls at the same rate, absent some upward force.

Yet, bullet trajectories routinely show the bullet rising after being shot, before then dropping. I don't doubt that for a moment...but am puzzled as to how that is managed. In my simplified (and obviously wrong) mental model, the bullet would be dropping from the instant it left the barrel and would never rise.

So, I am missing something fundamental. Is there lift created by the spin? Some standard design/production convention calling for a given upward angle so every barrel has a slight upward tilt when the gun/sights otherwise seem to be oriented horizontally? Some other effect?

Anyone who knows what's what, I'd appreciate a glimpse of the clue I'm firmly missing.

Yours is a common misunderstanding, and it is because we don’t realize that the barrel and therefore the “line of departure” of the bullet are angled up with respect with the line of sight.

Bullets are not lifting bodies like aircraft wings and therefore if the barrel were perfectly horizontal with respect to the force of gravity when the gun was fired, then yes, the bullet would start dropping below the boreline immediately and would never be capable of hitting a distant target. The way I illustrate it is to slide a coin off a tabletop and remind people that it starts dropping immediately when it reaches the edge. Same with a bullet if the bore is horizontal.

Most new trainees I’ve surveyed, even experienced shooters, believe the bullet rises above the bore line for a time and then starts dropping, but although it may rise above the line of sight, it never rises above the line directly out the bore.

Line of sight (eye to target):



Bore line (line of bullet departure):



Bullet trajectory that rises above the line of sight initially and then starts dropping down to the target:




So yes, that is correct:

quote:

Originally posted by joel9507:
[E]very barrel has a slight upward tilt when the gun/sights otherwise seem to be oriented horizontally?

That is why when zeroing sights we raise or lower them to change the angle of the upward tilt of the barrel. That is obvious with iron sights, but the same thing happens inside a telescopic sight.

use an AR15 for example.

the iron sight height is ~2.5 inches above the bore

so to get the bullet (starting out 2.5 inches LOWER than the lined up sights) to strike that Point of Aim ... the muzzle obviously has to be tilted ever so slightly upward... otherwise -- Point of Impact would never equal Point of Aim (line of sight)

SF's illustrations above are excellent depiction of this

simplest analogy is -- to throw a ball to your friend 50 yards away -- it has to be thrown in an arc as its falling to the ground the instant the ball leaves your hand. that's all the sights are doing -- creating a trajectory to maximally allow hitting a target at various distances

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two decent links here:

https://www.pewpewtactical.com...15-battlesight-zero/

https://www.thenewrifleman.com...st-out-of-ar15-zero/

you can get really far into the weeds on this subject which is why many - quite understandably - go with '50 / 200' and call it a day

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Ah, thanks to you both, the light bulb is now on, a little. Mister Newton can rest in peace again.

So, it's all about the gun being angled, if I understand correctly.

Rather than being a design feature of the guns creating the upward angle in the the bore line, it's because we orient the gun to put the sights on target, and the sights get set during zeroing based around what was required to have the bullets hit the target, at whatever upward angle that took.

After zeroing, that same upward angle automatically results from putting the sights on the target.

I may take a line level and a protractor to the range next time I take long guns out and see if I can get a sense of what sort of angles to the horizontal I have been shooting at.

Thanks again.

quote:

Originally posted by joel9507:
I may take a line level and a protractor to the range next time I take long guns out and see if I can get a sense of what sort of angles to the horizontal I have been shooting at.

That's not necessary, and it may not even help. Use the concept of bore sighting, for a rifle that is already zeroed for any distance. And I do mean any distance.

1 - Confirm rifle is unloaded.

2a - For bolt action rifle, remove bolt.
2b - For AR15, remove lower, remove BCG.

3 - Clamp rifle/upper in some type of vise.

4 - Compare aiming point of sights to aiming point of bore.

And now for some technical stuff on bullet drop. Let's assume an AR-15, using 69 grain SMK bullets, 2600 fps MV, 8000' air Density Altitude. Which is what my 16" barrels do with FGMM 69. Start with a ballistics program where sight-over-bore height can be set to 0", or at least a fraction of an inch. Set the zero distance to something really short, say 1-10 yards.

With these assumptions, the bullet drops about 2.5" by 100 yards. Using an AR15 with a common sight-over-bore height of 2.5", this means the bore is pointed 5" over point of aim at 100 yards. A 5" drop over 100 yards is roughly 5 MOA. Thus, the bore is pointed roughly 5 MOA above the sights.

One MOA is 1/60 of a degree. 5 MOA is 5/60 of a degree, or 1/12 of a degree. This is a pretty small angle that the barrel is pointed upward, in relationship to the sights.

quote:

Originally posted by fritz:
... 1/12 of a degree. This is a pretty small angle that the barrel is pointed upward, in relationship to the sights.

Thanks, that thought exercise and the math therein brings home the idea that estimating via a protractor and a level (nowhere near precise enough) would only have confirmed my innate (and incorrect) sense that the barrels were pointed horizontally.