View Full Version : .308 trajectory question

Arizona Fusilier
October 2, 2004, 10:16 PM
Round in question is the Federal 180gr Nosler Partition, out of a 22" Remington BDL.

If I'm zeroed at 25 yards, and 5" high at 100 yards, where am I back on? 250? Maybe 300?

Please, I'm not trying to make this a long-range sniper rig, so I don't need the "why don't you try .270/30-06/7mm/lazer beam)" (besides, I probably have it, and zeroed that too) :cool:

I just want to get an idea where I'm back on zero. Sorry, couldn't back the target up that far today. :o

Jim Watson
October 2, 2004, 10:29 PM
My Sierra ballistics program says if you are 5" high at 100 yards, you will be zeroed at 305 or thereabouts. You will also be over 6" high at 175 which might cause trouble if you pulled one a little high at shorter range.

October 2, 2004, 10:31 PM
without knowing the muzzle velocity the answer is indeterminate.

October 2, 2004, 10:46 PM
If you were dialed in at 25 yds and shooting parallel with the grd and level with the point of aim, the impact point should not have risen further out at 100 yds. Are you absolutely sure it was dialed in at 25 yds?

October 2, 2004, 11:35 PM

Your post suggests you haven't sighted in a rifle. Since the scope is several inches off the bore, when you put the crosshairs on the point of impact it forms an angle: The bore line and sight line converge at 25 yards, then diverge after that.

The rest of it happens because the sight line, being light, is a perfectly straight line. The bullet follows a ballistic curve. It starts below the sight line, converges with it, continues to rise through it, then comes back down to intercept the sight line again, then falls below.

If your scope and bore were perfectly parallel, the bullet would start about 2" low at 25 yards and just continue to drop out of sight after that, which isn't too useful.

Even without the precise velocity, the standard tables for the caliber will probably be within 10 yards or so.

Arizona Fusilier
October 3, 2004, 03:32 PM
Handy-yes, given the problematic variables of range estimation, etc., that occur under field conditions, an educated swag within 10 yards is usefull enough, and is what I was looking for. Sorry if I mislead anyone with an over-expectation of precision.

Jim W., thanks for the info, which WAS more detailed than I expected. Reckon' I oughtta' get my hands on a ballistics program, too. :)