Shooting at a 45-90 angle in tactical match (bullet impact)

So I'm well known on Sniper Central, but thought this was a better question for the AR guys.

I shoot 3 guns and tactical rifle matches on a team. Every match we shoot, the stages force us to shoot with our guns tilted an angles left to right, and some time prone with the rifle laying 90 on its side. I'm in a heated debate with one of my fellow team members as to where the bullet impacts with the rifle tilted to the side.

Some details on how our rifles are set up. We all zero at 50 yards, and shoot our own loaded ammo so we know we are also zero at 200. We are 1.25" high at 100 yards, and about 2" low close range. The last match we shot, all of our slanted shooting was at 10-15 feet, all but 2 head shots we had to take at 50 yards (prone, shooting under barricade with rifle laying on its side)

So I'm thinking at 15 feet, with the rifle slanted to one side, the bullet still impacts 2" to the bottom of my EoTech. So if the rifle is laying on the bolt catch side, the bullet impacts 2" to the right of the center dot on my EoTech.

My Team member thinks that with the rifle laying on its side, the bullet still impacts 2" tword the ground from the sight. So with the rifle laying the same way, it would still impact 2" to the left (relative to the optic).

I know this is hard to enplane in words, and I have looked threw google, and the forums hear, but have not found anything about this. If you can help explain this better, or even draw a diagram as to bullet impact to sight picture, that would be fantastic! I can draw something up and post it if it would help show what I'm talking about.

Please help!

Thanks,
Stephen

Maybe the graphic here will help.?

Short answer - You are correct when talking 10-15 feet . At a true 90* cant, bolt catch down / port side up, you will be about 2.5" to the true bottom hash of your EoTech, or your impact will be to the right of the dot. Things change as distance increases. Go out and shoot it. Easiest way to show him.

Longer answer - Same theory applies to a scoped bolt / precision rifle with a height overbore offset of the optic. The AR just happens to be about 2.5 inches.

On a traditional vertical rifle hold the muzzle or bore axis is oriented in a slightly upward direction in relation to our sights to intersect the line of sight. With the AR and your 50 yard zero, you have a crossing of the line of sight on the ascending branch of the bullets trajectory and another on the descending branch from the max ordinate of the bullets trajectory. BTW, for your 50 yard zero, you really should be having an outer zero right around 220 yards or 200 meters depending. This normal vertical hold of the weapon and if we forget about the elements, the trajectory we only need to worry about is the linear rise and fall in one plane. Canting other than 90* creates other issues.

Now, if the AR is bolt catch side down or port side up, 2 things happen.

First, the bore axis is now giving the bullet a trajectory heading to the left in another plane (no longer upward) in an attempt to intersect intersect our line of sight.

The second thing that happens remains constant no matter what, which is that gravity starts to pull the bullet downward as soon as the bullet leaves the muzzle.

So what does this mean from 10-15 feet? Since the muzzle is now facing at a left angle instead of an upward angle, you will be about 2.5" to the right of your dot (POA). Now if you equate that out to distance we need to start taking into account the trajectory of the bullet because of the effects of gravity. Up close, 10-15 feet, gravity is a non factor. Out to distance we need to account for gravity also as the bullet is traveling left and downward in a much different type of arcing trajectory than a traditional vertical orientation of the weapon. Basically from a perfectly 90* canted rifle, your max ordinate will be at the muzzle as the bullet has no upward trajectory. Of course things change when we shoot somewhere in between 90* and vertical.

Again the best way is to show him by shooting it.

Thanks all. Some good points, and confirmation of what I thought. We agreed today that we just need to go out to the range with targets set up from 10-100 yards, shoot a group upright, and 90' to one side (same side every time) and just see how much different it it out to some range.

I persnly think that with our 50 yard zero, we should still aim dead on at 50 yards, even if the rifle is laying on its side. I just don't think there is any noticeable bullet drop that close. Anything past that, I can see the bullet being impacted by gravity.

Your right, that its really about 220 yards with a 50 yard zero. I was still able to hit a 4" plate at 200 with my eotech set like this.

One thing I didn't think about tell now (and I don't know how much difference this would make), but my eotech is a lower 1/3 cw (I have the 516). I wonder how much that impacts the bullet impact at distance.

You are pretty correct with your 50 yard assumption on POA/POI if you are looking at hitting say a 4" target. There should be little variation at this distance. With a true 90* cant I might hold just slightly high on a 4" target and you should be good. Shooting 100+ is where you will start seeing the need for more correction on the same 4" target. But nothing beats setting up varying distances and shooting them.

When I talk about about cant error I come from the same community or school of thought as those on snipers hide and I am considering very long distance for precision. Cant error is not as big of an issue at the distances we are talking here. But the same rules apply when we take the AR out to distance also.

Here are some graphics that should help your friend understand cant and POA/POI even at 10-15 feet.





Light reading on Cant Error

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