Zeroing a rifle question..

[emcon5]

Drop a bullet and fire a bullet (same type) at exact moment will hit the ground at the same time??????

Yes, as a matter of fact, assuming the bore of the muzzle is perfectly level with the ground, and the ground is perfectly flat and large enough. Mythbusters covered this:
http://www.youtube.com/watch?v=D9wQVIEdKh8

If you drop a frizbee and throw a frizbee will they hit the ground at the same time?

I suspect if you threw the Frisbee perfectly level and dropped it perfectly flat they would. The reason it doesn't seem that way is that bullets are generally fired, and Frisbees are generally thrown slightly up.

A .308 drops about 2.5" from the muzzle to 100 yards. The reason you don't see that is because you are really aiming 2.5" above the target.

If the statement is true, then bullet BC has nothing to do with trajectory.

Of course it does. Well, indirectly. BC effects drag, which effects velocity, which effects trajectory.

 

[Big Pard]

My guess would be first decide on a cartridge/rifle then ask questions about zeroing it in. Velocity, Bullet Weight, Bullet Diameter, Bullet Profile, and Distance Shooting all play important parts in deciding where to zero a rifle.

 

[jimbob86]

IOW, IMO, zeroed at 25 yards is nowhere near good enough for reliable hits at 300. It's merely an easy way to ensure hitting the paper at 100 yards.

This^.

Since the .mil stopped teaching the average soldier to shoot well, hitting anywhere on a qualification silhouette, @50 to 400 meters, better than 60% of the time (IIRC) has been deemed "close enough for Government work"..... and that from the prone and sandbag supported positions.....