Bullet higher at long range

[LariatBob]

Help.

I have been shooting my AR for a few years now. I usually use a red dot sight.
I have been working on zeroing my Nikon 3-9x40 scope lately.
I am fairly new to this and I have a question.
Yesterday at the range, I put on the scope and send the target to 50 yards.
First 2 hits were centered but high about an inch or so. I adjusted the scope down one click and all was good. Centered hits all around the bullseye.

Then I sent the target out to 75 yards. I started hitting about 2 inches high.
I thought I might raise my tripod so I was sure not to be shooting "uphill" to the target. No change.

Then I sent the target out to 100 yards. The hits were a bit higher yet but not as big of a difference from 50 to 75 yards- as if the trajectory was flattening out.

I adjusted the scope down 2 clicks and was able to get nice grouping.

I did not return to 50 yards to check the effect. Ran out of range time and had to pack up.

Anyway, would someone with more experience please explain what is going on? Is my bullet actually climbing for mid yardage?

I need to return to the range and repeat, making sure all of my findings stay the same and verify that my scope did not shift or other mechanical causes.

Anyway, thanks for your feedback, I hope to learn something.

Bob

[Hoser]

Your bullet is climbing so much to get a 50 yard zero that is has not stopped climbing yet.

Depending on how high your scope is above your barrel, you wont be back on a zero until 175-200 yards.

[funkfool]

Hey Bob...
Glad you got some range time yesterday... indoors will spoil you!

Anywho...
You know that bullets follow a parabolic arc when they leave the muzzle...
They pass through the sight plane as they rise to their highest point and then they drop back through it on the way to the ground.
Check the Norma Ballistic calculator here:
www.norma.cc
Click the british flag for English then the ballistic tab..ballistic US
It will launch a ballistic calculator...
then, I presume you are using a 55gr jacketed bullet..
So select "Jaktmatch cartriges"
Then select ".223 Rem full metal jacket 55 gr"
Then adjust your zero range yds (the red line) to 25 yrds...
Then bring the distance line to 50 yds - and you'll be 1.4" high w/ 25yd zero
You can see then, that you would be quite a bit higher at 75 yds (2.6") and a bit higher still at 100 yds (3.5")... but just about sighted in at 300.
(If your height of sight line is 1.6 in)
Then compare that to a 50 yd zero.. etc...

(There is someone here who could give you the math on it..)
But this is a great visual of the effect and how to calculate what zero to use.

[esaabye]

Pretty simple really, since the scope is mounted above the barrel the sight line and the line of the bullet are different. Add to that the bullet will drop with gravity.

When you zero for a distance you are picking a point where the two intersect but the trajectory of the round will continue down range. What happend is the bullet crossed the 50yd mark at your line of sight but then continued on it's path that took it 2-2.5 inches above you sight line at the 125 yd then back down to sight line near 200 yds.


http://www.ar15.com/forums/topic.html?b=3&f=18&t=328143

[LariatBob]

Thanks, All.
Makes perfect sense. I guess I just need to put it where I want it......

Funkfool, see you on Thanksgiving.

Bob

[funkfool]

Thanks, All.
Makes perfect sense. I guess I just need to put it where I want it......

Funkfool, see you on Thanksgiving.

Bob

You bet LariatBob... I'll be bringing goodies.. can't wait.
Got a dremel?

[LariatBob]

Yep. Do we have some work to do?
Trying to get a brew ready for the day, I think I'm gonna come up a bit short on time. Waited too long to get started. Oh, well, it will be ready for Christmas...

[funkfool]

Yep. Do we have some work to do?
Trying to get a brew ready for the day, I think I'm gonna come up a bit short on time. Waited too long to get started. Oh, well, it will be ready for Christmas...

It's possible... It's possible...


Also - your BDay gift FINALLY came in...

[rondog]

Here's a picture to illustrate the bullet arc and line of sight. Pretty exaggerated, but it's a good visual aid to see how the line of sight is straight, and a rifle barrel is angled to "lob" the bullet to a distant target. Also how the bullet crosses the line of sight twice, and "climbs". It doesn't actually climb, of course, it's just how the barrel is angled.

We all know this, but a picture is nice. It's easy to see now why a rifle zero'd at 200 yds will hit high at 100 yds., etc.

[Tim K]

Here's a link you might find useful. Probably more information than you want, but reading it would be an excellent start to understanding your rifle.

http://www.globalsecurity.org/milita...-9/c05.htm#5_2