Range finder displays correct distance only out to about 140 yds & won't pickup targets at further distances

Bushnell Scout DX Rangefinderis my favorite one. It's a fantastic range finder.
It's offers some amazing feature and specification like...

• 6x magnification
• Range between 5-1000 yards
• 3-volt CR2 Battery
• Rangefinder Accuracy 5 yds

The Bushnell Scout DX Rangefinder will help you to pick from 3 different user modes by pressing the Mode button at the left side of the unit. First is the usual mode which can be used for most purposes up to 1000 meters and works well towards the pretty reflective surface.
When turned on, the Scout 1000 Laser Rangefinder liquid crystal display (LCD) will directly display icons like the bow and rifle mode. The bow mode will provide you with true horizontal distances from 5-99yd away, depending on the angle. The rifle mode, however, will permit you to get the angle and drop/holdover of your shot to the target from 100-800yd.

Rangefinder essential things for hunting. There are many rangefinders are available on the market. Here I give 3 best range finder for hunting lovers.
Sig Sauer Kilo 2000
The Sig Sauer Range finder yields 7 x magnifications which are the best thing any hunter would want. It allows you to focus even on the smallest target possible and never lets you to miss a shot. The 1000+ yards range works efficiently.
The Sig focuses on maintaining a high standard in its material. The solid body of the rangefinder is built with magnesium with soft rubber adjusted to the top and bottom so that you do not lose the grip. The materials used are lightweight and durable also.
Leupold RX-650 Laser Rangefinder
The Leupold RX-650 Rangefinder is Lightweight, compact and weatherproof that is flexible to carry and protect the display when you need to go for hunting. Keep eyes on our Leupold Laser Rangefinder review, and learn quickly why you should spend some time to assess the usefulness of the product.
Bushnell 202442 The Truth Rangefinder
Bushnell 202442 the truth rangefinder is a very portable and convenient product. It has been made in such a way so that you can take it quickly for shooting or hunting. The rangefinder has been made with quality materials and tested extensively. The materials used are well-built and durable without any doubt.

The attractive vertical design of the Bushnell G-Force DX is a combination of high technology integrated with some features in demand that is noticed on different Bushnell models also having a 6x magnification that can be utilized both for bowhunting and rifle hunting.
Fully Loaded
Display - The Bushnell G-Force DX is featured with VDT (Vivid Display Technology). Its red screen display has incompatible with the black screen display which is targeted for their budget customers. The settings for the intensity of red display is manually adjustable to one out of four preference settings. These brightness settings aid the user to adjust with the reticle and give a visual record or display of the output from the device of their preference under any condition of lighting.
MOA and MIL - The G-Force DX displays the readings about angle indemnified relics in mil or moa and the holdover in an inch or cm when the Rifle mode is turned on. Users can set the relics to measure in an inch, moa or mil when the ranging requires in yards. Again, users can set the program to show holdover data in Moa, MIL or cm.
Angle Compensated Readings - Some of the older versions of Bushnell rangefinders displayed the view distance in line or dots at the time of Bow or Rifle mode. Next, the device displays the shooting angle and extends the number. When in Bow mode, the G-Force DX provides the compensated angle range in yardage. Otherwise, it gives the relics information when in the Rifle mode. But, the newer version of the Bushnell displays the readings of site distance at first, then it displays the shooting angle beneath the screen for not more than one second and a half before disappearing from the screen. Eventually, the device provides an important information about angle compensation.
ESP 2 - The G-Force DX rangefinder is featured with the second generation extreme speed precision processor offers precise distance measuring advantage and boosted with speed. The device can provide up to 1/2-yard accuracy out to 199 yards and 1/10-yard display precision out of 125 yards.
Housing - The Bushnell G-Force DX is coating rubberized for easy grip with a metal housing. The length of the metal housing is 4 inches, thickness 1.3-inch and height 3-inch which is a compact design of the rangefinders. This dimension of the G-Force DX allowing it to give a relatively low weight of 8oz.
Range - The Bushnell G-Force DX is a vertical-style rangefinder used for long range shooting and the maximum range of the rangefinder is 1300 yards on highly reflective objects. An expected reading on trees under good conditions is up to 900 yards where the same on deer is maximum 600 yards. But, the flat style Bushnell 1600 Elite is the right one for the users requiring more ranging power.
Legend Legacy
The new G-Force DX is developed from Bushnell's previous G-Force 1300 hundred design. Although this model is a new design, it had to leave backward many wanted features of the Bushnell Legend 1200 version. The new Bushnell G-Force DX is a featured with a Bow Mode, Rifle Mode, and Regular Mode same as its forerunner. Another feature is the VSI (Variable Sight-in) that adds versatility in shooting with the rangefinders set with integrated ballistics charts. At last, the popular Brush and Bullseye targets priority settings has added a new dimension into the new G-Force DX.
Modes
Rifle Mode - By selecting the Rifle mode, users can pick a ranging sight that they prefer. After that, they had to select from a ballistic chart that closely matches the flight path of their bullets holdover. Then the rifle icon will appear at the left-top of the screen confirming that the device is in rifle mood. After ranging the target, the line of sight yardage will appear on the display. The device will display underneath the shooting angle which will be disappeared within a second and a half, and at last, it will display a holdover measurement in any unit of cm, inches, MIL, or MOA
Regular Mode - In this mode, the user will get a line or dot of distance view in yardage from the target and it will facilitate the users in no other ways. That means, the indemnified angle in yardage, he relics data or the shooting angle - nothing can be calculated or displayed.

Maybe they are too far away

None of them as it is to low a magnification to get a precise range from
the only way to check is to measure out distances to targets at the ranges on the side wheel and decide

You sight it in by firing at a target. Place the target at 100 yds distance if that is where you want it set for. Then you use the knobs to adjust the aiming point so the bullets strike where you place the crosshairs. This can involve a lot of shooting, and it is best to use a bench so you don't get confused by inaccurate handheld shots. Once sighted in, there may be other knobs to adjust for different distances or windage. These should be set to a central or neutral position while doing the initial siting, or maybe set to the distance you are siting in. My sights don't have such luxuries, so I am not sure how they work.

You have to sight it in and then insert the ring for the specific ammunition and distance you are using. From then point on, you can dial in the distance and the cross hairs will be right on.
It isn't an actual range finder, it's a bullet drop compensator.

Here's what you need to know about Mil Dots and rangefinding.

When you look through the scope you should see 5 mil dots on each axis, your scope may have broad lines taking place of the 5th mil dot if it is a "modified" mil dot scope. For measuring purposes, 1 mil is the distance from the center of one dot to the center of the one directly above or below it. 3/4 of a mil is the distance from the top of one dot to the bottom of the one above it, or the "space in between dots". 1/4 mil comprises a single dot, the space between the top of one dot and the bottom of that same dot.

A quick calculation is Size of Target (In Yards) x 1000 / Size of target in mils = Range in Yards

Miliradian or "Mil" is an angular unit of measure, so if you were shooting at 1000 yards and moved up 1 miliradian that would be one inch impact moved up.


Anyway lets say you have a 30" target and we need to find the range... using your scope you place the bottom of the target at the CENTER of a mil dot and count how many mils up, good estimation is key... I'll draw a little text diagram, an asterisk * will be the target top and bottom, and parentheses () will be a mill dot
( * )--------(  )-----*---(  )
Now lets assume the asterisk on the left is the bottom of your target and the one on the right is the top, I put Ten Hyphens in between each dot so if you count from the left you should get about 1.6 Mils. Its real easy to do it in your head, you already know two whole dots is one mil so you just have to estimate whats to the right (or top if you were looking down a scope).

So we know the target is 30" and we have a Mil Reading of 1.6
30/36= .833 so 30" is .833 Yards

So now we can use the equation .833 x 1000 / 1.6 = 520.6 Yards is the distance of the target


Now you can also use Mil dots to do hold over for when the target moves or for wind and elevation but that gets extremely complicated.


Parallax in Rifle Scopes is explained here 
http://www.6mmbr.com/parallax.html


There are many books and websites to confirm what I've said here, but the best way is to go out to your range and talk to some long range shooters and show them your rifle/scope etc and get hands on help.
 

I had the same problem, rangefinder would work only sometimes and only at short distances. Called customer support and was ready to send it in. Tech guy told me to turn off "First Target" ( or "last target") and turn on"LOS" (line of sight). Range finder now works perfectly at all distances. Apparently the first target feature doesnt work properly.