JW is correct. Nitro uses different combinations of shot size, as well as just one size in their shells. A mixture of two shot sizes (example 4x6.... read 4 AND 6) is called a DUPLEX load... a 4x5x7 (4, 5 and 7) would be a TRIPLEX load.

Remington does still load a 4x6, and used to load some very odd combonations such as BBx2 and 2x4.

Most of the patterns you see that have 200-300 hits in a 10" circle are at the hands of Nitro shells... mostly because #7 shot is very small and very numerous. In a lead pellet, a #7 shot likely would not have the energy to kill cleanly out to and past 40 yards... however, with a hevi-shot pellet, its just like shooting a lead #5.... thats part of what makes their shells so nasty on turkeys.