30-06 ballistics

[cbrgator]

At a 100-yd sight in, is the bullet still rising when it hits a 100 yd target or has it reached the peak in its trajectory and begun to fall?

 

[Ben Shepherd]

Depends on whether you sighted it for a 100 yard zero. If so, yes, it's all downhill from there.

If you sighted for a 2 or 3 hundred yard zero, it's still on it's way up.

 

[eric.cartman]

It all depends how much higher your scope is above the barrel...

If it's very close to the barrel, the chances are the bullet is falling already. If it's higher, the bullet is still climbing.

Do this... draw a gun and target on paper, with a line of sight from gun to target. Then draw bullet trajectory. Now increase the distance from the starting point of the bullet (end of the barrel) to the line of sight (end of the scope / sights). you'll see what I mean.

 

[cbrgator]

Yes, I was assuming a 100 yd zero. My scope is close to the barrel. At about how many yards does it start falling?

 

[JesseL]

You will almost always zero a rifle so that the bullet strikes the target on the downward portion of its arc.

The bullet starts out below the line of sight (obviously), crosses the line of sight at something like 45 yards (depending on the height of the scope and the particular load etc., I assumed a typical 150 gr .30-06 load and a 1.0" scope height), reaches the peak of its arc around 70 yards, and descends to the line of sight again at 100 yards.

You can play with the numbers yourself using a ballistic calculator like this one:
http://www.remington.com/products/ammunition/ballistics/remington_shoot_ballistics_software.asp

 

[cbrgator]

So if its sighted for 100 yds and I'm aiming at something 50 or so yds away (like a boar) I don't really need to do any compensating.

 

[Jst1mr]

If you want to get technical,

The bullet begins falling (in relation to the extended line described by the bore) the instant it leaves the barrel.

 

[FlyinBryan]

i use this site a lot

http://www.eskimo.com/~jbm/calculations/traj/traj.html

 

[Art Eatman]

The bullet is subject to that ol' debbil gravity as soon as it leaves the muzzle, as Jst1mr said. (I explained about trajectory and all that to my son when he was maybe eight or so. For years, the family joke was about "grabbity". Hey, makes sense.)

Zeroed at 100? I'd hold a smidgen low at fifty yards, if something mouse-sized was the target. It wouldn't matter for deer or hogs. Probably wouldn't make any difference on a coyote, for that matter. You're generally gonna be within an inch of the line of sight, once you're out past somewhere in the 20-yard vicinity.

I messed up one time, all tangled up in brush and trying to kill a hog at about ten feet. Totally forgot about the scope's height above the bore of the rifle, and shot low; shot the jaw off the hog. Big mess fire drill.

 

[CB900F]

Cbrgator;

Jst1mr is correct, the instant the bullet is no longer supported by the barrel, it starts to fall. However, the reason the bullet rises and arcs is that the barrel and sight plane are not parallel. The sight plane, what you see through the scope, is a straight line to the target. The barrel is ramped up at the muzzle, the breech being low, compared to the line of sight. That's where the arc to the target comes in. That's why you see midrange elevation figures given in ballistic tables.

900F

 

[rcmodel]

The biggest question is, why would anyone zero a 30-06 at only 100 yards?

Sight it in 2 1/2" high at 100 and it will be very close to zero at 200, and only a few inches low at 300.

rcmodel

 

[cbrgator]

I know how physics and bullet trajectories work. I know the bullet starts to fall after it leaves the barrel but is rising in relation to the ground because it is pointed up to counteract gravity. I just wasn't sure about the shape of this particular trajectory. I was just trying to figure out where a 50 yd shot would hit when the rifle was sighted in at 100 yards. And now I know so thanks guys!

 

[Vern Humphrey]

If you are sighted in for 100 yards, the bullet is falling at that range. It reaches maximum ordinate of around 0.87 inches at 85 yards and then begins downward.

Now technically, the bullet is always falling -- as soon as it leaves the muzzle. When we zero a rifle, we ajust the sights so they point down. In order to aim at the target, we must elevate the barrel, so that it points at an upward angle.

So even though the bullet is falling when it leaves the muzzle (that is, there is a downward component in its trajectory) its velocity allows it to rise. Eventually gravity overtakes the upward vector imparted by the launch angle, and the bullet begins moving downward.

Added: At 50 yards, a .30-06 (this is one of my handloads, with a 180 grain bullet at 2,800 fps) will be about 0.16" low -- assuming a scope sight with line of sight 1.5" above the bore line.

 

[shadowalker]

A lot of ammunition manufacturers publish estimated ballistic tables for their ammunition.

If you are hand loading you can create an estimated ballistic table with the help of a loading manual or you can do it online at a variety of places,

Hornady has an easy to use tool at http://www.hornady.com/ballistics/ballistics_calculator.php