AJ....question?

[snapper]

Bear with me... A few guys and I got into a discussion about sighting in a rifle and crossing the line of sight etc etc...

If you sight in your deer rifle (say a .270) dead on at 100 yards...that is the second line of sight, correct? It should hit dead on again at the first line of sight somewhere around 30 yards, correct?

My question is...do you know what distance a bullet would hit dead on (using a .270, 130gr.) if your sighted in (first line of sight) at 100 yards? If the bullet is still rising at 100 yards...where would it hit again at when it drops into the second line of sight?

Is it even posible with an average scope and rings?

[AJ]

Hey Snap,
Yep, bullets drop from the instant they exit the muzzle since there is no longer a force applied to them. Velocity starts to drop the instant it leaves the muzzle. Granted its miniscule, but it still counts. Therefore, we have to have our aiming devices on a different plane than parallel to the bullets path. With your typical .270 Winchester shooting a 130 gr bullet, the bullet drops about 2" at 100 yards relative to the muzzle. So to hit where we aim, we have to move line of sight (LOS) or aiming point lower. This will allow the bullet to rise and fall on out aiming point at whatever predetermined range we have selected (sighted in).

Using a typical sight height if 1.5" which is normal for hunting setups, and our .270 Winchester load, if the POI is dead on at 100 yards, the bullet peaks from 65 to 105 yards. This is where it crosses LOS. Using this setup, it will only cross LOS once. You can extend it a bit using see through mounts. If they will give a sight height 2.5" above the bore, you can zero POI at 100 and it will be zero from 95 to 125 yards.

If you raise the sight height, you can move the first LOS crossing. The max my ballistic software tools will go to is 10" above the bore line. Using a 10" high sight, and zeroing POI at 100 yards, the bullet is indeed on its ascent. It will again pass LOS at 400 yards. It will have peaked at 255 yards being 6.4" higher than LOS. But at 25 yards, its 7" below LOS.

Hope this explains it clear enough.

[Jeramie]

Wow, that is entirely to much thinking. I swear a puff of smoke just drifted out of my ear....

Good answer Aj. That is one question I had never though of but it really is pretty interesting. I had never grasped (or even thought) the conception that we have to raise the Point of impact to get a dead on shot at close distances. I knew that was obvious at longer distances but I never gave it much though on anything under 100. I guess if gravity starts to play its game immediately you have to be slightly above target on just about anything.

[snapper]

[ QUOTE ]
The max my ballistic software tools will go to is 10" above the bore line. Using a 10" high sight, and zeroing POI at 100 yards, the bullet is indeed on its ascent. It will again pass LOS at 400 yards.

[/ QUOTE ]

Yep, that sums it up for me...thanks! I work with some real maroons.