In the past couple months I have been plinking with my .223 Remington. I first worked up an acceptably accurate load at 100 yds. I then found my MV using an average of many rounds shot through my chronograph. I then plugged that MV, along with enviormental conditions, into my ballistic program (BulletFlight iphone app). I used those outputs to verify my trajectory at 450 yds. I started here thinking that the effective range of the .223 Rem cartridge is limited. In my mind a 600 yd groundhog shot with this rifle would be a feat in itself. Keep in mind this rifle will only be used for groundhog hunting, shorter range coyote hunting, and steel plate plinking. My 450 yd varification was a success and the round proved to be quite accurate. So last night I put some steel out at 675 yds. This plate was a square foot in size. When taking my first round sighter shot I was amazed that it struck a full 5.7 MOA low. By my calculations thats about 40"! After a redial and one more sighter I was on target and grouping around 1 moa with no problem. I don't expect the rifle to do much better than that at that distance but I can't understand what caused my program to be that far off. I am also unsure of what to do to correct it. If I tweak my MV in the program to the 675 yd validation it will throw all shorter range outputs way off. Any thoughts or suggestion would be greatly appreciated!