Ballistics Puzzle

BIGALSURF · 12-05-2005, 07:22 PM

I have a "see through" scope mount that ends up with the centerline of the scope over the centerline of the muzzle by 2 inches versus the standard 1.5 inches. So here's my puzzle, here's the ballistics of the bullet I was shooting, a 150 grain .308 Winchester by Hornady , boat tail spire point, and here's their ballistics, based on a typical 1.5 inch difference between muzzle and scope.

Muzzle 100 yd 200 yd 300 yd 400 yd.
-1.5 inches 1.9 in 0.0 -8.4 -24.9
2820fps Vel. 2560 2315 2084 1866

But I sighted in 1 inch high at 100, and the scope is mounted 2 inches above muzzle centerline. So what are my heights at the distances? Can't figure this out. At 100 yards therefore their total difference muzzle to scope is +3.4 inches over the muzzle line, while I am at +3 over the muzzle centerline. Where am i at 200 300 400?

(If you say lost you're right!)

NORMAFAN · 12-05-2005, 07:46 PM

There are many variables to the ballistics of a certain load. If that is published data you can be even farther away from knowing what you will shoot at 400 given a 200 yard zero. The only way to know where your gun is going to shoot is to shoot it at different ranges. Besides if you are planning on shooting at 400 yards you should practice at that range out of respect of your quarry and yourself.

Yeti · 12-05-2005, 08:26 PM

Even with scope mounted at 1.5" over the bore you must shoot the different ranges to get your guns ballistics. I have a ballistics program and find that most of my loads are 1-3" different at 200+.

Washington Hunter · 12-05-2005, 09:51 PM

Big Al: I sent you a private message.

BIGALSURF · 12-05-2005, 10:06 PM

I'm not "trying to shoot at 400" I'm just trying to figure out the bullet's path. I missed at about 250 and I think I went low if you want to know! I wasn't shooting at 400.

Rank Amateur · 12-05-2005, 10:10 PM

Put up a bigger target. You should have been close if you were holding dead on, within 10 inches anyhow.

MarlinMark · 12-05-2005, 10:37 PM

Big Al,

The key to knowing your ballistic path is in the velocity of your projectile. It's easy to know the weight to the grain, the Ballistic Coefficient, and other factors that play into the bullets path (humidity, elevation, etc) but the biggest piece missing from your post is the velocity of the projectile at (or really close to) the muzzle. Here is a program that takes "sight height" into consideration, as well as everything else you could want to factor in.
http://www.eskimo.com/~jbm/ballistic...raj_basic.html

I hope this helps,

Mark

BIGALSURF · 12-06-2005, 06:55 AM

Thanks, this will help a lot, I did post velocity, 2820 fps at muzzle. Also, can't "put up" a bigger target as the one I missed has four legs and trotted away unharmed!

BIGALSURF · 12-06-2005, 07:05 AM

Used the program, it's awesome, and I was right, I shot under, I didn't have it sighted in high enough at 100 yards, only 1 inch and I should have been about 2 inches. Back to the drawing boards. Thanks again!

Hunt'nFish · 12-06-2005, 09:06 AM

BIGALSURF,
My recommendation would be to NOT rely on ballistics very much w/o having the TRUE velocity and true measured BC. The published velocity can vary a lot from your actual velocity. Especially on longrange calibers. They get the published velocities from SAMMI Mininum demension test barrels. The typical factory barrel turns in signifigantly slower velocities.
For every else (.30-06 and under) just zero it at 200 and shoot it at 300 just to check drop, at 150 it should be about 3" high and at 250 be about 3" low. Your thinking way too much.

If you shoot the rifle at 100,200,300yrds and record drop, measure the muzzle velocity and record the altitude, temp and humidity, I can give you a corrected BC for your load.
Hunt'nFish