Leupold RX Rangefinders

[AJ]

Check out the new Leupold RX Laser Rangefinders. They not only use the laser to measure distance, but they have feature called True Ballistic Range that tells you the actual shooting distance when your shots are uphill or downhill. This allows you to make a more precise aim on target. Pretty knifty. I saw them in the Cabelas Shooting Catalog and nope, they aint exactly cheap.

[snapper]

Re: Leupold RX Rangefinders

huh...thats interesting, I thought that the laser shot a straight line to the target...wouldn't the measurement be the same?

If I point my range finder up or downhill and range a target...isn't the laser shooting straight to the target? Wouldn't that be the yardage you'd shoot it for?

Maybe I will learn something new here.

[AJ]

Re: Leupold RX Rangefinders

If you are shooting hard angles uphill or downhill, you need to know the horizontal distance between shooter and target, not the line of sight distance. Gravity works straight down, not angles up or down a hill. If you measured 300 yards LOS with a typical laser and the angle was 45°, and the shooter held for a 300 yard zero, the bullet will hit high.

I guess the rangefinder uses an inclinometer to measure angles and you have to plug in the approximate speed range of you bullet. The readout will tell you what the shot should be aimed as.

[AJ]

Re: Leupold RX Rangefinders

Here is the true math version of what I was trying to get across above:

The theory as to why the bullet always shoots high for uphill and downhill shooting is based on the projectiles path in relation to the pull of gravity. Gravity works perpendicular to the horizontal line. It's the horizontal distance traveled by the bullet that is important rather than the actual linear distance traveled.

According to the rules of trigonometry the cosine of THETA is equal to the horizontal range divided by the slant range (hypotenuse). By rearranging the terms, the horizontal range is equal to the slant range (hypotenuse) multiplied by the Cosine of THETA.

Assume we have zeroed a rifle at 300 yd on a level range and we are shooting at a target on a slant range of 300 yards. Assume the slope angle THETA is 30 degrees. The cosine of 30 degrees is 0.87. The horizontal range for the bullet is only 261 yards (300 * 0.87). In order to hit the target we should hold the gun as if the target were only 261 yards away not 300 yards. If we shoot where the scope crosshairs intersect the target we will shoot over the target. In the field, you probably don't really know the slant range or the slant angle very accurately. Just remember to always aim lower, because any slant range shot, either downhill or uphill, will be higher than if it were a horizontal shot.

[snapper]

Re: Leupold RX Rangefinders

Yeah...I understand (sorta ) the math and gravity involved in shooting uphill or downhill...guess I don't really understand how the range finder knows your ranging uphill or downhill and at what angle. I assumed it would just range a straight line and thats the distance...then would be up to the shooter to know his/her equipment and adjust for the shot.

[AJ]

Re: Leupold RX Rangefinders

The range finder probably has a inclinometer built in. It could be as simple as a wheel with a weight on one section of its circumfrence. As the rangefinder is raised or lowered the wheel will move since the heavy portion will be aimed to gravity. It can be a simple rheostat and the voltage drop will be plugged in to a chip with the logic of x many millivolts = x many degrees. It computes the angle and spits it out to a display. Its actually pretty simple, now that I think about it. "Why didn't I come up with that? DOH!"

Anyhoo, here is a graphic representation of what its calculating. This is what the math from my above post is figuring out. The red arc is the same distance line of sight (LOS) from the shooter. The uphill angle is exactly that. The LOS to the target is still 300 yards, but the horizontal distance is less.