For your consideration one Thomas RBRF4 bullet 254 Confederate 3 ring bullet. You will find this bullet to be in excellent dug condition. The patina is a near perfect white color that has a slick, waxy feel to it. Mold seams can be seen on both sides of this bullet. Notice the elongated nose, 3 shallow cast rings & a heavily out of center (eccentric) cavity this bullet type has. The cavity is parabolic...all of these bullets are just like that.  Measures about 0.525 x 1.01 inches.

Danny Spencer once shared this information with me. McKee & Mason bullet 409 0.577 calliber-(Fayetteville arsenal bullet?)...see notes opposite page found in diameter .520, cavity 11-3 (parabolic).  I have never seen one of these bullets with a cone cavity. 

Is this a little brother to a M&M 409?