Shooting up/down hill question

[pvauto]

I'm new here and so far have got a lot of info off this site. Just last week I took out my AR in 223 and was shooting in like a 40deg angle about 240yrds. I have my gun dialed at a 50/200yrd zero but it was hitting about 5-6" high and drifted due to the wind (55gr boolits). My question is how was it hitting so high when it should be dropping? I'm new to hunting and doubt il ever take a shot past 100 but with a variation like that it can be a difference of a clean kill to even a miss. I have a lot of time shooting at p2k so I know it's accurate. On a side note I'm from east county San Diego and I want to start shooting long distances and maybe somebody can be somewhat a mentor? I have a 300 win mag that I would love to be able to stretch her legs

[AR15barrels]

When shooting at an angle either up angle or down angle), you are reducing the effect of gravity on the bullet.
Gravity pulls towards the earth so the effect on the bullet is strongest when your billet is flying parallel to the earth.
Any ballistic calculator will factor in the angle-of-fire for you.

There are also quick and dirty methods to adjust your dial for angles using an angle cosine chart or indicator mounted on your rifle.
The cosine gives you a percentage of adjustment.
You can either scale the distance to target, or you can scale your amount of elevation dial.
As an example, a 45 degree angle gives a 50% correction factor.
If you need to dial 0.6 mils to be on your 240yd target on level ground, you would dial only 0.3 mils to be on your 240yd target when the target is 45degrees above or below you.

[thegiff]

45° is .7 correction, so .6 mil horizontal = .42 at 45°

60° is .5 correction, so .6 mil horizontal = .3 mil at 60°

[gau17]

/\ /\ /\ Damn Asians.

[pvauto]

ok im slightly loss lol so as of now i think i have to take 45*and do cos 45* and that equals the correction of .7 so what do i do with that now? my scope is a burris fullfield 2 that uses moa

[Short Action Precision]

Shoot lower!

[Stoopy]

ok im slightly loss lol so as of now i think i have to take 45*and do cos 45* and that equals the correction of .7 so what do i do with that now? my scope is a burris fullfield 2 that uses moa

Take your normal elevation and times it by .7. Example I'm shooting my 308 at a target 1000 yards away at an angle of 45*. My normal dope is 9.6 mils. So it would be 9.6x.7=6.7. I would dial 6.7 mils on my scope and take the shot.

[Stoopy]

MOA version is the same just MOA.
34.5 x .7 = 24.15 so dial 24.25 MOA

[thegiff]

The best way is to correct the distance with the cosine of the angle. So, if you range 600 yards line of sight, and you shoot up or downhill 45°, then the drop range is 600*cos45° = 424 yards. Then, use the 424 yard number against your drop chart.

The end result is that the bullet doesn't drop as far as your line of sight distance shows, so you need to aim lower or dial less drop.

However, windage corrections are for line of sight, so use the 600 yard windage dope for your wind.

[rksimple]

The best way is to correct the distance with the cosine of the angle.

Wrong.

http://www.exteriorballistics.com/ebexp ... icle1.html" onclick="window.open(this.href);return false;

[buffybuster]

If you are indeed shoot in at a 40 degree angle, either up or down, the Line of Sight distance is 240 yards, the Horizontal distance would be 184 yards. Gravity acts only on the horizontal distance. The greater the angle, the less Horizontal distance is for gravity to act on the bullet.

This is not taking into account the effect of gravity on the terminal velocity.

[gau17]

Wrong.

http://www.exteriorballistics.com/ebexp ... icle1.html" onclick="window.open(this.href);return false;

Good reading material. Thank you.

[Mobius38]

My head hurts!

To many words need pictures!

[pvauto]

thanks for the replies! i definitely have some homework to do lol im not new to shooting but i am new to learning the science behind it. i figure the more i learn the better i can shoot. i couldnt find any of this just researching online

[thegiff]

I re-read the Sierra link that Ryan posted, (last looked at it a few years ago) that calc comes out way closer than the one I posted.

Equation terms are:
Drop = bullet drop relative to barrel, always a negative number
Path = bullet drop or position relative to scope crosshair
Angle (theta) in degrees

Corrected Path = abs value[Line of sight Drop] * [1 - cos (theta)] - Line of sight path

Example:
1000 yards 308
horizontal drop = -440.24"
horizontal path = -398.61

at 45° angle up:
Corrected Drop = 440.24*[1-cos45] - 398.6 = -269.66"

I've edited this post a couple times... Looking through sierra's equation, they are using a drop number that is not output with jbm's normal output. The drop number is from the barrel relative to itself and not to the scope, and is always a negative number. You also need the drop relative to the scope crosshair.

This would require another set of numbers on a dope chart, or of course would be much easier with a ballistics app.

[thegiff]

OK, I've screwed around with JBM to make it output some data that could be used in the sierra equation to get a good angle correction, here is an example:

Taking my .243 at 2940fps, 1000 yards
0°, drop relative to scope = 296.5" (called "path" by sierra)
Using JBM to calculate, we find that at 45° the result should be 199.3" drop (called "path" by sierra relative to the scope

To get the "drop" data from JBM, set zero distance to 1 yard and scope height to 0", and from the resulting drop chart at 1000yd we get 334.5"

"path" = -199.3"
"drop" = -334.5"
Theta = 45°

Corrected drop (in the scope) = 334.5(1-cos45) - 199.3 = 198.5"