Mr. Poop,

I have a copy of "Outdoor Life Field Guide" from 1990.

In it, a guy talks about how if you sight your rifle in at 25 yards, you should be able to hit what you're aiming at all the way out to 250 yards.

Taking a 180 grain 30.06 for an example, if it is dead nuts on at 25 yards, he says it should be 1 inch high at 50 yards, 2&1/4 high at 100, 3/4 inch high at 200 and 2&1/2 low at 250.

You ever heard of anything like this?

In the Marines we used 30 and 300 yards for the same thing.

Yes, indeed. I imagine it would depend heavily on your load, but a truly horizontally fired bullet will create lift and in fact arc upwawrds for a good duration of its flight.

~Zero the Inestimable

If you make an elevation(vertical) adjustment on your rear sight you change the angle that the gun is from line of sight. So if you make an adjustment to shoot a few hundred yards out you are tilting the barrel up just a little bit. This causes the bullet to rise above the line of sight. The numbers that you gave are where the line of sight and bullet path intersect for that particular load.

Thanks fellows, I understood most of what you said before I asked the question, but my real question was "if you're dead nuts at 25, shouldn't your bullet be dropping from then on?" I understand ballistics fine, and if ALL your targets are set to the exact same height (say 5 feet), I'm thinking you should register drop through all of them after the 25 yard one. The bullet starts to drop due to gravity just as soon as it leaves the barrel.

Unless your shooting position (lets make that a table 30 inches tall) is lower than your first target position (30 inches lower, in this case) you should register drop. The guy doesn't say this in the article, but that is the only way to get the arc necessary to do what he says.

I'm wondering just where in relation to your target you need to be to sight in using this method. Any ideas?

If your barrel was perfectly horizontal you would have drop the whole way. However, you almost never shoot with your gun completely horizontal. What I was talking about is that the barrel is tilted usually a fraction of a degree when you look through the sights. The bullet then travels above horizontal, while your line of sight stays horizontal.

It's hard for me to explain, so I'm sorry if I'm just rambling on.

When you fire, the round will take an arching trajectory, for example like rlpinca said, when you fire at a target that is 30 meters, the bullet will be going up when it strike the target. at a certain point in space, the bullet will start to fall, and at 300 meters the bullet will be the same height as it was at 30 meters.

If I had a picture it would be easier to demonstrate. Note that the reason the bullet rises is due to recoil. hope this helps

It rises because the barrel is pointed slightly upward while looking through the sights. It's not lift, because there is not pressure differential on top and bottome of the bullet. And it's not because of recoil, because recoil only acts on the firearm and the shooter.

Ripinca.

I don't know if you can totally rule out lift from the bullet. I've been taught, by my marine TO, and the instructor at the range, that the bullet, due to it's shape, and the fact that the air is seemingly more dense to a fast moving bullet, then it does lift a little in the initial stages. I've been told that the effect if far more pronounced with a carbine, rather than a rifled barrel, but have not tested it myself, so can't say.

We mark at 25 yard, and with out military round, we end up looking at a level shot again at the 200 yard mark.

RipSlider

Lift is created when a shape causes a pressure difference. Low air pressure on top due to air moving slower than the bottom of the shape. The bullet is symetrical so I don't see how there can be a difference. Something I just thought of though is that the spinning from the rifling could do something for it.

Thanks again.

I think the lift would be negligible just from the bullet. I don't think the rifling imparts enough roughness on the surface of the round. With a golf ball the dimples give it a laminar airflow and the spin does give it lift, but the grooves from the rifling don't bite in that deep, and the bullet is spinning with the axis of travel, whereas with a golf ball the axis is across the direction of travel. If anything, the lift generated would make it move to the side.

I think I understand what the guy was talking about now, but until I put it into practice, I still wonder.