It is called a "Maxi-Ball," made for blackpowder rifle shooters/hunters, from the second half of the 20th-Century and still being sold today. See photos below. The waxy yellow stuff in the body-grooves is bore lubricant, which as you see, comes already applied on these bullets when you buy them at a gunstore instead of casting them yourself in a Lyman (modern-made) bulletmold.
As photo #3 shows, there are several body-styles of Maxi-Ball.
And yes, the name is a deliberate play on the old Minie-ball name.