Forfree,you can go on Hornady's website and use their ballistic software.
They offer a printable cheat sheet of s small,useful size.
You can vary the parameters you input per youraltitude and the weather forecast.
I don't own an I-pod or smartphone, but there are ballistic apps.
I do not have a Leupold CDS scope.Leupold told me they are as precise and repeatable as target knobs. You get 15 MOA to play with.
I have mixed feelings about ballistic reticles. If we are talking boiler room shots ,IMO,the Boone and Crockett can be useful,but 600 yds is a stretch.The B+C combined with CDS gives you options.(And costs money)
I own the Pride-Fowler RR800 reticle in a fixed 10X scope. Kind of busy,very fine lines.Requires good light.I find it takes eye discipline/focus to use.
As Mark pointed out,it can only be "right" for one set of conditions with one load. I think the stakes matter some. A coyote is different than a once in a lifetime sheep hunt.
If you want to use a reticle for 600 yds,zero it at 500 or 600 yds. Use sofrware to minimize error.Verify your other ranges with targets.
Error will tend to minimize at shorter ranges.I'm saying if you zero at 600,the error at 200 may be acceptable,If you zero at 200,the error at 600 may be amplified to unacceptable.
,If your reticle is based on a 168 gr 308 at 2680 fps at sea livel,etc..in yards,it won't be right at 6000 ft.
But those marks will be right at SOME range maybe the 400 mark will be on at 450 yds.If you know that,you can work with it. Same with the wind lines. The 10 mph line might be correct at 12 mph. That's still useful.
Once you have all that dope figured out for your reticle under one set of conditions,you can use ballistic software to "warp it in" for a different set of conditions.
My eyes are getting old,cataracts,etc. Its hard to use the Rapid Reticle. I can do a Boone and Crockett,but I would not do a 600 yd game shot that way.
Maybe 400 on a confident day. Understand,a 250 yd prairie dog is usually a hit.I have luck shot PDs to 600 I had a lasered 1100 yd spot wher,for fun,I've shot some nice targets after a couple of spotters.They'd all be in the vitals of an elk,on a good day.But for myself,(not telling You how to live) I find the variables more manageable inside 400 yds. Inside 400 yds,a fairly flat shooting rifle,including a 308, is pretty manageable for trajectory.
Inside 400 yds,a Boone and Crockett can work well if you shoot it enough to sort it out.
For a minimal amount of ready ballistic info,you can write it on a paper plate with a marker,then used a photo copier to reduce it so it will fit in your ocular scope cap.
I don't evenknow what Leupold is making these days. My variX 3 2.5 to 8 Mildot and my 3.5 to 10 B+C have served me well.