Who's got a understanding of distance shooting? 600 to 900 yards.

Not familiar with the .223 but IMO the smaller the bullet the more prone to air densities and wind etc.. the farther down range. 600 + yards is a way long shot and a smaller bullet has lost its advantage at velocity vs bigger calibers in the distance equation when mass becomes a factor. The larger bullets retain more energy and stability farther, allowing a more forgiving flight in unforgiving conditions. So in a nutshell grab your .308 and do the longer shots, every caliber has its limits. All can kill at distance, but accuracy as we all want; becomes less with "less" bullet at distance.:twocents:

You probably don't want to here this but the answer to your question is yes you do. Barometric pressure, Altitude, and Temperature all play a large roll in long range shooting regardless of caliber. Most rifles I work loads up for shoot best up against a maximum load, so never work up a load for any rifle on a cold day, high altitude, or extreme high barometric pressure and expect to shoot it on a warm day at sea level. That could be a recipe for disaster. A lot of ballistic programs are available to suit your needs. If you have an i-phone you can download i-snipe, enter the information for your load,and the current atmospheric conditions and it will give you the proper hold over for the condition's. I personally shoot a 270 WSM necked down to 243 dia. It has a 32" Krieger barrel and shoots a 95gr. Berger VLD with a BC of .524 @ 3635 fps. Zero @100yds it falls 14 moa.@1000yds. For predators it is awesome, but I would never go to the field without my i-snipe due to the fact that conditions are constantly changing. Hope this helps, Happy Hunting