DWM,
The formula that the angle function in the ballistic programs use is as follows:
Path in inches = P - (1.0 - C * D)
Where:
P = Path of bullet at level fire in inches.
C = Cosine of angle.
D = Total bullet drop at range in inches.
Increase in bullet path height:
5 deg .004
10 .015
15 .034
20 .060
25 .094
30 .134
35 .181
40 .234
45 .293
50 .357
55 .426
60 .500
Multiply the total bullet drop at the actual range by the number above fo a given angle, subtract this amount in inches from the bullet path at level fire. This will now be the new bullet path for that angle.
This is how they calculate it, I'm still not sure why the multiple they use happens to be 1.0 minus the cosine of the angle.
* * *
DC,
The kills are not in question, like I said. What happens to be, is the precision and repeatabilty of the sighter shot(s) and kill shot.
For one to put 3 rounds on POA at 2000 yards for instance, 2 sighters and 1 kill shot, what does it take to do this?
Lets take a look.
For round numbers sake, I'll use a 20" x 20" kill zone to illistrate this, close to an Elk anyway.
A rifle capable of shooting sub 1 MOA 3 shot groups should do it right? Hypothetically, yes, in the real world, no. It's not going to be anywhere linier at 2000 yards. Even 1000 yard shooters will tell you it isn't linier there either.
How small will your rifle print three shots at 2000 yards?
Variables associated with each of the shots, reguardless of if a sighter or two is taken:
Muzzle velocity ES.
Ballistic coefficient ES.
Variables associated with the sighter shot(s) themselves, reguarding rezeroing the rifle at the target distance:
No Russian laser rangefinder, Lieca Vector, B&S or Wild, and you're probably screwed from the start.
Spotter does not have a measurement method to determine how far POI is from POA, or an exact way to convey POI location to shooter if shooter does not see the hit.
This is if the spotter can even identify the POI in the first place. 2000 yards with 20x eye pieces is, well, a long friggin ways still.
POI to POA adjustment after a sighter fired requires shooter to again line up on original POA and dial reticle to POI location to zero on sighter, or possible to a location in between two or more sighters fired.
This brings up a problem with zeroing off of a single sighter, or possibly two, and them calling the rifle perfectly zeroed. Sorry, it ain't so. You very well could be zeroing off of a shot that's POI was unusually low, high, left or right. The next shot, or two may very well be in a completely different location within the group... thus the rifle is not zeroed at all, just close. But how close?
Well let's see... If you zero the rifle on a shot that was at an exteme low (low shot in the MV ES maybe), you're now are suceptible to missing the animal completely if you have another shot that shoots low in a group for some reason. The more shots you fire to sight in on, the less possibility of this happening. Still very likely with only two sighters to zero by tho, just one makes it even more likely. If this weren't the case, at 1000 yard BR, they'd never make use of 10 sighters, now would they.
Now, while you're doing all this fiddling around taking sighter shots and dialing the reticle in to POI, the wind does have time to change, very easily plenty of time too.
At 1000 yard BR, these guys have the benifit of a target with calibrated rings, so when a bullet hits, they know how many MOA off it is with a quick look back at it, not so with the stump, bare patch of ground or what ever the sighter is fired into in the field. It has to be guaged some how before the sight adjustment takes place, this takes a few seconds to determine and adjust, at least a few seconds.
Then if you're smart, you look to see if the wind has changed in any way out to the target, more time. You fire a second sighter to verify, possibly, and if you're quick you get on to see how far it was off, still no way to measure it, but a good guess works. Now you either adjust again, and or swing to the animal, one last look for a wind change, and fire the kill shot if not...
The sighter shots do help in some ways, but the method has serious downfalls as pointed out. It's not without problems, by any stretch of the imagination.
The explanation often given for how the method is employed is really quite a limited one and very misleading to anyone that's not thought the whole thing through with some knowledge of ballistics at LR.
I once thought it seemed to be a great method, but the more I learned about ballistics and what really happens at 1000 yards and beyond, the flaws in it really couldn't be ignored, as they seems to be by others. But then again, I know more than half the guys on this site are savy enough to understand what I've just outlined.
With only one or two sighter shots, I'm not confident it works as accurately as it's cracked up to, much less at 2000 yards. The facts just speak to clearly.
Enjoy your hunting method tho, I do mine.
[ 11-29-2003: Message edited by: Brent ]
I fully understand about log books and data sheets. 99% of the shot I've taken over the last 10+ years are in my log books. I have a chart for just about everything and there not done from a computer, but from actual shots in the field and on the range.
