AR Sight Offset / canted weapon question

So, today at training a debate arose: what, if any, effect on accuracy or point of impact does canting a weapon have?

Not taking precision bolt guns or anything, but talking about AR's with red dot sights. If cant has negligible effect up close, what range would effects start to show?

Also talking about canting anywhere from 10 to 90 to beyond degrees.

My thoughts were that if my rifle is not canted during zeroing, but is then shot canted 90 degrees... there would be a change in point of impact. This given the same aiming point each time regardless of cant.

Help? Diagrams I can blow up their email boxes with?

 

 

 

 

Joined:      14 January 2010                Location:     Lobster emoticonMAINELobster emoticon

Original Post
For 90 degree cants - We typically held higher on a pectoral or lower on a shoulder to obtain a center mass hit when using barricades / cover and concealment and engaging enemy from 100-200 meters.

100 Meters = Upper Pectoral Hold

125-200 = Shoulder Hold

For a 45 degree cant, effects are halved.

For targets beyond 150-200 meters we typically assumed a better shooting position.

We didn't bother with any cant less than that as effects were negligible at the above ranges.

This is easily proven on a flat square range shooting groups with different cants and distances.

Mike Pannone's M4 Handbook probably has something about this as well, I'll dig through my copy when I get home.

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This is also a good resource:

 

http://www.riflescopelevel.com/cant_errors.html

 

I don't have the numbers like F2S does, but the application is pretty basic:

 

Aim high and to the side the mag of your gun is oriented;

 

If you cant the gun to the left, meaning the mag is sticking out to the right, the bullet will hit low and to the left -> aim high and to the right.

 

And vice versa.

 

Here is a vid where I shoot a 9-hole drill at a steel torso target at nearly 200 yards, applying this principle:

 

https://www.youtube.com/watch?v=q0yP8dbKSBA

 

Yeah, I know, I missed an easy port.....sue me! 

It's not about surviving, it's about winning.

My shorthand for 90degree cant is this:  hold towards the magazine well and "up" (skyward) to account for the path/drop of your bullet. 

 

Example - if I wanted my POI to be the mouth of a target, I may hold on their eye, depending on which way I had the gun canted...

 

Depending on the gun/optics you're shooting, you may start to notice it past 50yds; 100yds is where both induced errors really start to become evident, IMHO. 

 

Best way to deal with this issue is to live-fire it at the range.  Get yourself a blank target backer, stick a clear aim point on there and try out different cants at various ranges, marking your groups after each run. 

Originally Posted by KUTF:

Best way to deal with this issue is to live-fire it at the range.  Get yourself a blank target backer, stick a clear aim point on there and try out different cants at various ranges, marking your groups after each run. 

+1.

 

I did this and it's very enlightening.  It's one thing to read about what happens, another thing entirely to storyboard it out.  

 

This also applies to seeing the deflection from resting your barrel on/against objects or barricades.  At 50 yards, a center chest hold with the barrel resting on the barricade can cause rounds to be over the head.  

 

Great visual tool for teaching classes also.  

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Thanks dudes. It isn't so much that we disagreed on being able to hit the target while offset, as much as "some people" denying that it would have any effect at all. 

 

I guess this was kind of a stupid topic/question, since I myself knew the answer, and was apparently seeking validation. 

 

 

The debate centered around if you basically put the rifle in a vise straight up and down, chose an aim point and fired a group, rotated the rifle 90 degrees (say, clockwise) and readjusted so the aim point was again on the same point as before and fired another group. Repeat two more times. I don't think I was articulating well that the aiming point would be on the same spot every time, as opposed to adjusting to compensate for cant.

 

 

 

 

Joined:      14 January 2010                Location:     Lobster emoticonMAINELobster emoticon

If the point of aim was the same, you would have a change of POI, because the bore axis is at an angle to the sight axis, to counter gravity.

When you zero the gun you either depress the sight axis to shoot further, or elevate it to shoot closer when adjusting the sights; when you then hold your gun to shoot, ie going back to a horizontal sight axis, the angle of the bore axis will be affected accordingly.

However, if you were to hold the bore axis at the same spot through your experiment, you would have the same POI.

It's not about surviving, it's about winning.

What I had learned that seemed to make the most sense to me was -

"What this boils down to is that the bullet will cross the vertical sight plane (not the horizontal sight plane) closer to the muzzle (though not by a whole lot, depending on zero distance). It will be slightly low at close range because the bullet will essentially be launched horizontally instead of at a slightly upward angle and will therefore begin "falling" immediately upon exit from the barrel." - taken from the m4 thread.

It was a interesting discussion at training since I thought the general idea was kinda common sense but hard to explain without just doing it (like lobster continually asked that we just try during the lunch break).

For min of man I guess a high chest hold will work and a little movement toward the mag, especially as distance increases seems to be what needs to happen.

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