| From: | shadowrn@*********.com (Marc Renouf) |
|---|---|
| Subject: | Ballistics 101 |
| Date: | Thu Apr 18 13:40:01 2002 |
> I can verify that bullets fire in an arc which is why you have to site in a
> rifle based on the distance you are planning to shoot. If you site in your
> rifle at 300 yards then shoot at a deer at 100 yards, you will hit high on
> your target. I don't know what causes the arc (lift sounds good to me) but
> I know it happens.
Gravity is what causes the arc. The bullet is affected by gravity
as it travels, meaning that even if it is fired perfectly horizontally, it
will still accelerate towards the ground as it flies.
You line of sight, on the other hand, is just that: a line.
Basically, all you're doing when you sight in a rifle is making sure that
the parabolic arc that the bullet will travel in will intersect the line
of sight of the scope at a specified distance. If the target is actually
closer than the sighted distance, the shot will land higher than expected.
If the target is farther away, the point of impact will be below the point
of aim.
Depending on the muzzle velocity, calibre, weight, and shape of
your bullet, its behavior will change. Depending on your load, you could
have radically different ballistic characteristics. Sighting your rifle
in for 55 grain 5.56 NATO ball ammunition will mean that you point of aim
will probably be off if you're 50 grain hollowpoints. And the amount that
it's off will vary with distance.
This is why snipers are very particular about ensuring consistency
in their loads. Further, they tend to practice a lot, so that they can
get very accustomed to how much drop, holdover, windage, etc to account
for when firing. It's very good sniper practice to keep a log of your
shooting conditions so that you can more accurately determine where your
bullet is going to land. Even things like the humidity of the air the
bullet is traveling through can drastically affect ballistic performance.
If anybody's interested in this kind of stuff, I would recommend
something like "Sniper/Countersniper," or "The Tactical Marksman."
Both
are good references and contain some good explanations of ballistic
principles and how different conditions affect them.
Marc Renouf (ShadowRN GridSec - "Bad Cop" Division)
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