3.5x4 where did you get these #s. If they are from the top lid of your shell box they refer to 3.5 dram equivalents of black powder and #4 size shot. This does not mean your ammo is loaded with black powder just that the powder is equal in strength to 3.5 drams of black powder. The usual sequence of #s would be the shell length ,dram equivalents, shot size.IE 2 3/4- 3 1/2- 4 Hope this helps.