.30-06 Trajectory Question


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cbrgator
January 25, 2008, 03:26 PM
Lets say my .30-06 is sighted in at 100 yards but I was going to shoot something considerably closer, say 25 yards. How, if at all, would I have to compensate for that? What is the bullet rise/drop at 25 yds?

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Vern Humphrey
January 25, 2008, 03:40 PM
Basically, zero hold-over and -under.

To understand this, remember the bullet starts dropping the instant it leaves the barrel. If your sights were aligned parallel with the bore, the bullet would start out lower than the line of sight and get lower as it goes down range.

To compensate for this, you adjust the sights so they are looking down, relative to the bore line. When you aim at a target, the result is the bore is tilted up, and this makes the bullet actually rise above the line of sight some distance from the muzzle. As it goes downrange, though, it is continually falling, and finally gravity overcomes the upward vector imparted at launch, and the bullet crosses the line of sight again.

This second crossing of the line of sight is the range at which you are zeroed. For most highpower rifles, at most common zero ranges, the first crossing occurs about 25 yards from the muzzle, give or take a few feet.

cbrgator
January 25, 2008, 03:44 PM
Ok, so around 25 yds I should be dead on...
but say around 50 yds I should actually aim slightly lower because the bullet will be above where my crosshairs were aimed, right?

Vern Humphrey
January 25, 2008, 03:53 PM
Yup -- that's called "mid-range trajectory." Most people zero to hit a bit high at 100 yards -- the actual zero range is from 200 to 250 yards, depending on your preferences. For large game, little or no hold-over or -under is required out to around 250 to 300 yards.

The first crossing will still be at around 25 yards, give or take a foot or two, regardless.

Mr_Pale_Horse
January 25, 2008, 03:55 PM
No. Unless you are hunting field mice.

Given a deer sized target for example, you can choose to hold dead on the center of the heart lung area (which measures ~8" from top to bottom) and with a rifle sighted 2.5"-3" high at 100 yards, your bullets will strike somewhere within that 8" height out to 250 yard+

Dead is dead. No style points awarded for heart shots.

rcmodel
January 25, 2008, 04:02 PM
The thing is, the trajectory of the 30-06 is so flat, the bullet would never go above the line-of-sight at 50 yards with a 100 yard zero.

Assuming a scope sight mounted 1 1/2" above the bore:
With a 100 yard zero, the bullet would still be about 1/2" below the line-of-sight at 50 yards and still going up to reach zero at 100.

At 25 yards it would still be about an 1" below the line of sight.

With a 200 yard zero, it would be about 1/2" high at 50, and about 1 1/2" high at 100 yards.

http://i81.photobucket.com/albums/j219/rcmodel/KTOG/1224.gif
rcmodel

USSR
January 25, 2008, 04:15 PM
Ok, so around 25 yds I should be dead on...
but say around 50 yds I should actually aim slightly lower because the bullet will be above where my crosshairs were aimed, right?

Nope! With your rifle sighted in at 100 yards with a typical scope setup, you will be a couple inches low at both 25 and 50 yards.

Don

John4me05
January 25, 2008, 06:58 PM
I sight mine in at 50yds...
I am no more than 2" low from 0-200 (give or take 1/2" at 200)
300 i think is getting into the have to figure the range and where to hold as it is about 8.5 or so low.. but from 0-200 i hold center of the boiler room...

Diggers
January 25, 2008, 07:36 PM
Heh,:) short answer; Aim right at the darn thing because its not that small. :D

Jaenak
January 25, 2008, 08:21 PM
*Digs out his 99th edition of the Shooter's Bible*

Okay, lets see here...

A 30-06 Springfield with a 165 grain Federal Nosler Ballistic Tip bullet sighted at 200 yards instead of 100 yards will have the bullet drop of...

100yds. - +1.8in.
200yds. - 0
300yds. - -7.7in.
400yds. - -22.3in.

So unless you're shooting something the size of a ground squirrel, you can hold dead center to about 250yds and hold 10-12 inches high from 250-350 yards. I wouldn't take a shot an inch longer than 350 yards though. I might even draw the line at 325 for me.

Vern Humphrey
January 25, 2008, 10:25 PM
Yep. If you accept a slightly higher mid-range trajectory, and zero for 225 to 250 yards, you basically hold dead center out to 300 yards.

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