Micro Size Tribute to Bob Shores and his silver bullet engine. This is a running 1/3 scale model of Bob Shores 1/8th scale Silver bullet engine. The 22 caliber "Achilles" engine is 3/16" Bore and 1/4" Stroke 2 cylinder automotive style engine. This Palm size show peice won the 2005 Sherline Machinists Challange.