One more trajectory question for you.If you sight in at sea level,then recheck your zero at high altitude,should the point of impact be the same?If not why?Would any change be due to a change in muzzle velocity,or would it be due to other factors such as thinner air or a change in the effect of gravity.?

I have a feeling you know the answer to all these questions and you're trying to tease our brains. Well, it's working. I still want to know why scope height affects ballistic calculations and MPBR...if you know please tell.

As for this question....I don't know anything, but I would guess that at higher elevations, the POI would not be the same, and the reason for this would be a combination of all the things you listed. MV might stay the same, but Less gravity would reduce drop. Thinner air would reduce drag, thus increasing velocity. Cooler temps would reduce pressure, thus affecting MV...and the list probably goes on. Thanks for the brain exercise, and if you really do know the answer to this and the scope height question, please let me know...

Thanks,
Rob

As Big country stated in the other thread,the answer is simple geometry.Of course it is much easier to show someone than explain it in words.The best that I can do is to suggest that you look at a drawing of a bullets trajectory in relation to the line of sight.You will seethe line of sight originating from the sights or scope,and the bullet path originating from the bore.Now look where these lines cross,usually at two pointson the drawing.Now imagine that the line of sight started from further from the bore.If it still meets the bullet pathat the same firstpoint on the trajectory curve,will it still cross the bullet path at the same point the second time?The answer is no,since the angle between the line of sight and bullet path is now different,the second crossing will be at a different point as well.

OK, I think I am starting to get this...I am visualizing a line of sight (which is straight) and a bullet path (which is an arc). For simplicity, lets say the arc crosses the line of sight at 50 and 150 yds. And it reaches the peak at 100 yds...3 in. above line of sight. And it reaches 3 in. below line of sight at 200 yds. That means the Max Point Blank Range is 200 yds with the scope zeroed at 50 and 150. Am I tracking so far?

Ok, so now we raise the scope higher and angle it down, forcing the same 50 yd intersection of LOS and bullet arc. The second intersection would be beyond the original 150 yds...lets say its at 175. But in this case, the peak of the arc would be more than 3 inches above LOS. So, I can see now that you can't just say, "if I am zeroed at 50 then i am 3 inches high at 100" (for this example)...because your scope height may or may not allow for the correct LOS angle to make that true. But scope height will not infact change the MPBR. The LOS angledoes not affect actual arc path/shape.

So, scope height will affect POI, but it will not affect MPBR. Right?

So, the next question is...knowing the arc path of the bullet, how do you figure out proper scope height to get the most out of thearc? In other words how do I know where my LOS shouldbe in order to make the arc's peak 3 inches above it?

I amthinking that ultimately, scope height adjustments would only have minor impact on shots below 300yds? Minor enough to ignore completely for sporting purposes?

Thanks for making think through it, and let me know if I missed something.

I think you have it.

Oh my, I have to admit this burnt me on high altitude once. And forget 35degrees uphill. Hey what can I say, I was so excited I about had a heart attack.