Trajectory Question

[runway1]

All the trajectory tables I see have the bullet rising above the line of sight then dropping. Why? Is the barrel a few tick up from the LOS? Thanks!

[Reductio]

I'm assuming this is for an AR-15? Look at your gun, and you might notice that your sights are higher than your barrel. They're like that on most guns. The bullet starts dropping the second it leaves the barrel, so to get the best trajectory, you actually have to 'lob' it out there a bit.... so it will come from under your LOS and zero once, go above, then re-zero with your LOS at some point past.

[runway1]

So, you're saying the barrel pointing slightly up?

I have a .308 Remington 700P but I'm talking any rifle. I was just looking at tables comparing the .17HMR with .22WMR (yes, I know they're rim fires) and the tables show ~+1.5" at 50 yds and then back down.

[Nathan Krynn]

Technically yes.


The zero is where your sights and the trajectory meet. Before your zero it will be higher, after lower.

[Reductio]

So, you're saying the barrel pointing slightly up?

I have a .308 Remington 700P but I'm talking any rifle. I was just looking at tables comparing the .17HMR with .22WMR (yes, I know they're rim fires) and the tables show ~+1.5" at 50 yds and then back down.

Yep, since your sights are above the bore, the bullet will *always* have to rise to meet your line of sight, and the only way to do that is angle it up slightly. This is why people talk about .223's having a 25/300 yard or 35/200 yard zero... it zeros at both distances, is low before and after, and high in the middle.

[runway1]

Yeah, ok. It zeros just in front of the barrel and then later at your 100/200 whatever point. My 700P is zero'd at 100 yds. Ok, thanks all!

So the barrel's axis and the scope's axis are NOT parallel. That would then make sense.

[brando]

Ballistic objects move in parabolic arcs in the presence of gravity. It's not a straight line to the target.

[IntoForever]

The only exception would be if your sights zero was at the peak of the trajectory.

[NytWolf]

All the trajectory tables I see have the bullet rising above the line of sight then dropping. Why? Is the barrel a few tick up from the LOS? Thanks!

Simple answer: Because your sights are always above the barrel.

The line of sight, whether scope or iron sights, is always a straight line. The bullet's trajectory is always parabolic due to gravity. In order for the bullet to hit its target at the intended sight-in distance, the bullet has to rise to point of impact. In other words, the bullet has to rise from its starting point (in the cartridge) to the line of sight.

Most people sight in their rifles at 100 yards, which is well before the peak of the parabola. Because of the sight in, the bullet's path crosses the line of sight exactly two times.

[five.five-six]

The only exception would be if your sights zero was at the peak of the trajectory.

that is only useful if you are only target shooting at a fixed distance inside of point blank



in a 25/200 or 35/300 the bullet is always within about 2" of zero from the muzzle to ~450 or so

[shy 7th]

Ballistic objects move in parabolic arcs in the presence of gravity. It's not a straight line to the target.

UNLESS you are aiming directly at or away from the gravitational source.



...but most people will never find themselves aiming straight down or straight up.

[five.five-six]

UNLESS you are aiming directly at or away from the gravitational source.



...but most people will never find themselves aiming straight down or straight up.

it happens

[Fjold]

Here's an exaggerated picture to show how the barrel and line of sight relate.

[G-forceJunkie]

Its already been covered pretty well, but think of it this way. Gravity. Your line of sight is a straight line, typically level with the earth (unless you are shooting up or down a hill.) Gravity makes the bullet start dropping the instant it leaves the barrel. Unless you tip the barrel up a little bit, it would never cross your line of site.

[Army]

Think football. You and the receiver are on level ground. To throw it far, you throw it high.

Gravity affects the bullet the instant it exits from the barrel. To compensate this immediate drop, the barrel is angled upward to "football" the bullet to the target.