BDC scopes do work if your use them properly. You could put them on every gun your own if you want. However, the performance of the bullet will vary with each caliber; that is with your .308 you can get solid data out to say 800 meters depending on your ammunition andyour gun. On your .243 I would not stretch farther then maybe 400-500 meters. Again, depending on the quality of your loads. You NEED to get d.o.p.e (data on previous enguagement) for your rilfle system. For example, say your TC .308 is zeroed at 200 meters. You move to 300 meters and shoot a 3 round group....log that you held and the center of the 300 meter circle or whereever to get exactly where you wanted your group to be (log tht in)...at 350 meters...your held at the bottom half of the 300 meter circle...you can really split hairs with this. You HAVE to know what your gun and ammo will do at each meter line. With that said you have to use the exact same ammo. For the money you can buy scopes where you acutally dial in the exact yard line...that is...At 535 meters I will set my scope and 5+1...To be honest...get out there and shoot your gun with the scope you want at each yard line to get your data. I would put your scope on the .308 and shoot it.