This 30-06 Wildcat Cartridge was designed in the mid 1950s by R.E. "Rocky" Gibbs. It is a 30-06 cartridge case blown out with the shoulder angle increased and the neck shortened to increase the powder capacity.  Mr. Gibbs called it "The Worlds most powerful 30-06".
  The larger case capacity (an average of 7 grains more powder) give a 150 grain projectile a velocity of 3,285 (F.P.S.) vs. 2900 (F.P.S.) in the normal 30-06 loading.
  Unprimed 30 Gibbs Brass is selling online from between $1.98 to $2.20 per case (ie: $39.59 to $43.99 for a box of 20).