AR Ballistics/ammo query

[GeorgeStrickland]

I went shooting with my brother in law yesterday. He has a 24" barrel AR. We were shooting some 55gr 3250fps Russian ammo. It was dead on at 35 yds. We backed up to the max avaiable range of 70 yds and it was over a foot high! How can that happen?
Thanks,
Geo

 

[Stumper]

That sounds extreme but the sight line is so high on ARs that dead on at close range means high for a LOOOONG way out. You need to have the bullet path and sight path cross further out to keep the trajectory close to line of sight.

 

[GWMENT]

That sounds about right for an AR. One other issue you need to be aware of at all times is the concept called "know your weapon".

This is not an insult or a flame, it was beat into all vets at basic training, or at least is was when I went through boot.

Regardless of what gun you are shooting, there will always be a certain amount of "climb" in the bullet path before it crosses zero. Where that will be depends on the weapon, bullet, and powder.

There are several ballistics programs on the net that will show you the bullet path for a weapon, bullet and powder combo. Just search for "ballistic software". There are a couple that are free.

Enjoy.

GWM

 

[azredhawk44]

It was dead on at 35 yds. We backed up to the max avaiable range of 70 yds and it was over a foot high! How can that happen?

Can't be a foot high at 70 if it was dead on at 35, unless the sights are a foot above the bore of the rifle.

More than likely, it was about 2-3 inches high at 70 if it was sighted at 35, or else you sighted it at 15 and then shot at 70.

Sight convergence is a sub-topic of something called "Battlesight Zero."

Basically, if you zero an iron-sighted AR-15 at 25 meters, the bullet will rise above the sight plane and descend back down to re-intersect at about 300 yards. This is for military spec M855 ball ammunition. Other ammo with different velocity or bullet weight will be slightly different, but will be similar in principle.

 

[Niner4Tango]

I agree with the 2-3". Your 35 yards zero is very close to the 31m zero on pages 1 and 2 here: http://www.usaac.army.mil/amu/ServiceRifle/M16-M4%20data.pdf

I this were happening to me, the first thing I'd suspect is that I had changed my sight picture between the 35 and 70 yard set ups.

What kind of sights were you using?

 

[chasep255]

A while back I sighted my AR in at 25 yards and then it was like 8'' high at 50 yards.

 

[Kmar40]

I went shooting with my brother in law yesterday. He has a 24" barrel AR. We were shooting some 55gr 3250fps Russian ammo. It was dead on at 35 yds. We backed up to the max avaiable range of 70 yds and it was over a foot high! How can that happen?
Thanks,
Geo

The bullet is still rising above the sight axis. Basically the bullet will cross the sight axis twice. Once on the way up and once on the way down after gravity does it's thing. This is the best diagram I can find in a short amount of time.http://img.photobucket.com/albums/v601/waterhouse/02-trajectory.jpg

How high above bore was the scope mounted? I suspect it was pretty high.