I am having a hard time convincing an individual that in order to use a ballistics calculation,you must know the sight height.He insists that if you know where the point of impact is at 50 yards,you can use the calculation to find the point of impact at another range without knowing the sight height.He claims that different heights of rings will not effect the results.Your opinions on this?

I believe that you and sh. h. are not communicating.

You are saying you need to know scope height to put that info into your program to calculate trajectory figures. But you were talking in your post about how changing the scope heights would change the results.

I think sh. h. was thinking that somehow you were implying the fellow might shoot at 50 yards with one scope height then change rings before shooting at 100 yards or something.

Just a communication thing.
At least that is the way it appears to me.

Robin down under

quote:

I think sh. h. was thinking that somehow you were implying the fellow might shoot at 50 yards with one scope height then change rings before shooting at 100 yards or something.

So did you make the same assumption as sh h?I doubt it.But he stated very plainly that sight height was not necessary to use the trajectory calculation,did he not?I am asking the same question here so other people can interpret the question as they please and then give an answer.We will see what the opinions are.

I plugged in a 30 cal Hornady 150 sst into the JBM ballistic calculator here: http://www.eskimo.com/~jbm/ballistics/traj_basic/traj_basic.html

With a 2.5" sight height and a 1.5" sight height. Zero at 50 yards here are the two trajectories;

SH.......2.5"......1.5"
50 Y...0"........0"
100Y...+2.5"....+1.5"
150Y...+1.4"....+0.4"
200y...+1.7"....-0.3
250y...+0.6"....-2.4"
300y...-1.9"....-5.9"

"He claims that different heights of rings will not effect the results.Your opinions on this?"

Stubble,

You are, of course, %100 right.

Maybe it would help to put it this way:

"Imagine the scope has a height of 0 inches above the bore's centerline--in other words, no height at all. How then, could you aim at a target down-range (say, 100 yards)?

"Answer: You could not. You would have to aim above the target a couple of inches to allow for gravity; in short, you would have to 'rainbow' the bullet onto the target. The shooter would therefore be 'guessing' as to how much holdover was needed.

"Next, imagine the scope is one foot above the bore's centerline. The scope, being a full foot above the barrel, is aiming a 'lazer-straight' line at the bullseye. But the muzzle is one foot below the bullseye. The bullet therefore must climb one foot to hit the X.

"That's a pretty steep up-angle for just 100 yards. Imagine how far down-range the bullet will be when it crosses the scope's line-of-sight again on the downward path!"

It might help to draw on paper those two extremes. Otherwise, you'll need a physicist to give him a real explanation!

Good luck!

friar

quote:

Originally posted by stubblejumper:

He claims that different heights of rings will not effect the results.Your opinions on this?

If the bullet starts out 3" below line-of-sight, it will rise 6" before it is 3" above line-of-sight, as opposed to 4.5" if the scope if 1.5" above the centerline of the barrel. It will be a longer distance before it's 3" below line-of-sight again, and this extends your point-blank range at the cost of being 3" low at the muzzle. My antelope gun has the scope centerline 2.25" above the centerline of the barrel for this reason.

I made the same assumption as duffy and sh h. You were talking about changing the the height inbetween 50 and 100 yds.Sh h was talking about keeping the height the same. As duffy said its a communication thing.

I did not make the same "assumtion" as Sh. but it was a bit confusing reading his posts then Pb"s posts. Untill I looked them both over carefully and it seemed they were on different wavelengths.

I would like to see what ballistics program Sh. is using. Perhaps it is one where sight height is not a factor that needs to be plugged in. Then he may wonder why it was brought up and would not think it was important.

Robin down under