Long versus Short trajectory

[dalepres]

I am looking at the following quoted specs on a 30-06 cartridge. I'm confused by the difference between the Long Trajectory specs and the Short Trajectory specs. If I am zeroed to 200 yards and shooting at a deer at 500 yards, am I shooting 14.7 inches high or 50.5 inches high? And why?

Thanks,

Dale

WINCHESTER SUPER-X .30-06 SPFLD 180GR POWER POINT
Manufactures Number: X30064

30-06 Springfield
180 gr. Super-X® Power-Point®
Ballistic Coefficient: 0.438
Super-X® Power-Point®: Unique soft nose jacketed design delivers maximum energy on target. Notches around jacket mouth improve upset and ensure uniform, rapid expansion.
Rounds Per Box: 20
Rifle Ballistics

Distance (yds) Muzzle 50 100 200 300 400 500
Velocity (fps) 2700 - 2497 2304 2118 1942 1775
Distance (yds) Muzzle 50 100 200 300 400 500
Energy (ft. lbs.) 2913 - 2492 2121 1793 1507 1259
Distance (yds) 50 100 150 200 250 300
Short Trajectory (in.) -0.1 0 -1.3 -4.1 -8.5 -14.7
Distance (yds) 100 150 200 250 300 400 500
Long Trajectory (in.) 2.0 1.8 0 -3.4 -8.6 -24.9 -50.5

 

[41magsnub]

It assumes you are zero'd to be dead on at 200 yards, then shows how high you have to shoot at each distance. In this case you hold 50.5" high for 500 yards. That is long trajectory

The short scale does not even go out to 500 since you would have to hold it 8' high or something crazy like that which would put the target outside the viewable area of most scopes. Short is zero'd at 100 yards.

 

[dalepres]

Ok, I can partially answer my own question. I finally hit on the right search terms on Google to yield this result:

http://www.winchester.com/search/searchresults.aspx?searchtext=ballistics

For centerfire rifle cartridges, Winchester publishes downrange ballistics for two zero points. The majority of these feature a 100 (short range trajectory) and 200 yard zero (long range trajectory), although cartridges with shorter effective ranges are at shorter ranges.

I hadn't noticed that the two trajectories in my original post were based on different zeroes. The short trajectory is for zero at 100 yards and the long trajectory is for zero at 200 yards. Oddly, zeroing further out (200 yards) yields a larger drop in point of impact at 500 yards.

I'm better off zeroing the gun at 100 yards for the 500 yard shot.

By the way, be careful googling this. There is a spam/virus site that the google results page looked almost identical to the actual Winchester.com site. Thank goodness I'm using FireFox; it caught it without opening it. With IE, I'd probably be reloading windows right now. Make sure you open the Winchester.com site only.

 

[dalepres]

Thanks, 41magsnug. You saw more that I didn't catch. Even though there were the same number of entries, it is a different set of entries and only goes to 300 yards on the short trajectory. Now it all makes sense.

Not that I'd be likely to take a 500 yard shot anyway, but at least now I understand the options.

 

[41magsnub]

if you are going for a 500 yard shot you are much better off with the long trajectory zero. Compare the required hold over for any given range between the two scales. The short trajectory holds over roughly twice as much.

With a long trajectory zero you hold over 50.5", with a short trajectory zero it will be significantly more than that.

 

[Shawnee]

How about this... ?

Winchester Super-X PowerPoint 150gr.

B.C. .270 and MV = 2900fps.

sighted to "zero" at 275yds.


50yds. = 1.9" high
100yds. = 4.0" high
200yds. = 4.3" high
275yds. = 0.00
300yds. = 2.4" low
400yds. = 18.3" low
500yds. = 46.4" low

Use the same point-of-aim out to 350yds.

 

[dalepres]

That's a good idea, Shawnee. So why now zero to 300 yards?

 

[Shawnee]

why not zero to 300yds.?

You can but that will cause higher figures at ranges from 50yds. to 250yds. or so.

The goal of this type sighting (called "point-blank" sighting) is to sight the rifle so the bullet is travelling only a little above or below the line of aim out to the longest reasonable distance a person would take a shot at game.

For may modern calibers - a "zero" of from 250yds. to 275yds. will accomplish that.

As an example - a (generic) deer is 15" (+/-) from the bottom of the brisket to the topline of the back. If your aimpoint was the exact center of that distance, you would have at least 4.5" - either high or low - where the bullet could land and be very lethal.

Thus if the rifle is sighted so the bullet's path stays within 4.5" above/below the point of aim at any distance out to... say 350yds.... the shooter can not worry about "holdover" or "holdunder" for 95% of the shots they ever get.

Hope that makes sense.

 

[~z]

If you intend to take a shot at 500, I'd suggest you adjust the scope to 500yds. Additionally check your range finder to determine it is actually a 500yd shot. Then check your wind meter to determine if you are dealing with a constant wind, determine its value (direction relative to the target), make another scope adjustment if necessary, read for max and min values, watch for the conditions to stabilize, varify your readings with your buddy, discuss and differences, compensate, have partner back down the power on the spotting scope, and make the shot only when you are 100% confident it will be a DRT shot. Believe me it is difficult tracking from that distance.
The key to making shots like that is to practice it at the range. 500 may not be that far, but if you have not done it on paper, get closer. One nice thing about the long shot is you have plenty of time. Use it on the math.
~z