If you match them up to a good ballistics program using the actual measurement of there spacing they can be very accurate but if you mean dead on 100...200...300...etc for fifty different cartridges firing fifty different bullets in fifty different environments ............ Impossible. Personally I love Nikons bdc because it gives me thirteen reference points on the vertical axis but those ranges will vary depending on a wide variety of variables. Check out nikon spot on and it will give you a concept of what is practical with a given cartridge reticle combination. good luck P.S. For a specific cartridge and a specific reticle for that cartridge it should be close if the conditions are the same between real world and those the reticle is based on. IE weather, pressure,altitude, etc.
I have used them for years, both custom and factory pre-set ones. They really work, with an accurate rifle, quality rangefinder, and BDC reticle you can do some accurate shooting. The real key is PRACTICE!!! Shooting 1 gal milk jugs at different ranges from field shooting position is the best you can do! My daughter killed a NV Mule Deer at over 600 yds. with her Burris Ballistic Plex a couple of seasons ago. I killed an buck antelope at 661 yds with my Leica ER 3.5-14 last season. They work! NJS