Rifle Scopes Using reticle to range from elevated position

[rawdeal77]

I'll preface by noting that when it comes to scope ranging, I'm a newb with little experience, and pretty much everything I've learned came from this site or the intruction manual for my scope.

This past weekend I was scouting my new West Texas deer lease, where I was ranging potential shots from various locations using my scope (Vortex MOA/MOA). Some of these shots involve fairly high elevated positions requiring the gun to be held around 20-30 degrees from horizontial. This got me thinking about how such circumstances might effect the ability to accuractely range using my reticle.

Assuming a deer is 3ft (1yd) tall at the shoulder, he would be approx 2 MOA at 200yds (which is exactly the distence between substention marks on my scope). But doesn't this assume that I am on an even horizontal plane with the deer?

As a shooter's relative position to the deer increases in elevation, it seems the percieved height of the deer decreases. In other words, from an elevated position the same deer at a distance of 200 yds may appear only measure 1 MOA from the sholder. Is there a way to compensate or "guage" this effect? In other words how do you use mils or moa to range a target of a known height from an elevated position?

 

[Rob01]

Re: Using reticle to range from elevated position

You use the width of the target. It's usually the best way to range hanging steel as well as it's usually hanging on an angle so the height is off some.

 

[hrfunk]

Re: Using reticle to range from elevated position

Yep. You are right. As your elevation increases, the vertical size of an object will appear to diminish. The horizontal measurement, however, remains constant. Simply measure the object horizontally and you should be fine.

HRF

 

[CoryT]

Re: Using reticle to range from elevated position

You can also multiply the height of the object by the sine of the angle, then use that in the range formula.

Even a horizontal measurement is not perfect, since it requires the target to be perpendicular to the reticle. Any angle there causes the same problem, that angle is also much harder to measure with any precision.

 

[Rob01]

Re: Using reticle to range from elevated position

No width is not perfect but better than height if you had to choose between the two on an angle. I always try and do both on any target I am miling.

Better than both is a LRF

 

[RobertB]

Re: Using reticle to range from elevated position

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Rob01</div><div class="ubbcode-body">No width is not perfect but better than height if you had to choose between the two on an angle. I always try and do both on any target I am miling.

Better than both is a LRF

</div></div> Yeah, I don't think you should LR hunt with out a LRF. Deff past,300-400 yds. There is not way I would go out hunting without one.

 

[dcjs]

Re: Using reticle to range from elevated position

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Rob01</div><div class="ubbcode-body">No width is not perfect but better than height if you had to choose between the two on an angle.</div></div>
Rob,

curious as to why you would choose width over height with targets at an angle. With stuff that is upright (a hanging steel plate, a deer or a human) you can be prety much sure that your target is vertical, and you can measure the angle to your target (angle cosine indicator), while with width it is much harder to get an estimate of the angle.

Of course height involves other challenges like stuff that is standing in the grass and is partly obscured, but the angle problem in particular should be somewhat easier to handle because of the vertical nature of many targets and the fact that at least in principle it can be measured by the shooter.

 

[Rob01]

Re: Using reticle to range from elevated position

Because hanging steel isn't always hanging straight up and down. It can be at quite an angle taking off inches in it's vertical size. More so than any small width difference.

Adjusting for the shot with an ACI isn't what he was talking about but adjusting to the viewable section of the target from an angle. If you can't be sure your target is showing you it's full size you are using in your formula then your final number will be off. The width is usually more accurate.

As mentioned if I were hunting I would definitely use a LRF. It will give you a much more accurate yardage than miling the target. In matches if given the choice I use the LRF. If not then the reticle is used.

 

[dcjs]

Re: Using reticle to range from elevated position

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Rob01</div><div class="ubbcode-body">Adjusting for the shot with an ACI isn't what he was talking about but adjusting to the viewable section of the target from an angle.</div></div>
The ACI wasn't meant to be used for the final firing solution here (of course you will be doing that, too) but for the determination of a corrected target size given a known target height and elevation angle (what Cory was referring to). If I am, let's say 30° above my target, I can take the cosine of 30° and multiply it with the true target size to get a corrected "apparent" target size that I will see in the reticle (of course assuming the target is vertical) and use that corrected size for my ranging.

Of course this depends on the target being reasonably vertical, and as you have pointed out, that is not always the case.

 

[rawdeal77]

Re: Using reticle to range from elevated position

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Rob01</div><div class="ubbcode-body">You use the width of the target. It's usually the best way to range hanging steel as well as it's usually hanging on an angle so the height is off some. </div></div>

Thanks guys, I figured it had to be something simple.