Buchner logged his 300 combat mission on 27 August 1943, his 500th on 4 March 1944. Following his 500th combat mission, at the time credited with 13 aerial victories, he was nominated for Knight's Cross of the Iron Cross (). From 1 June 1944 to 1 August 1944, Buchner was appointed as Staffelführer (acting squadron leader) of 4. Staffel (4th squadron) of SG 2. As a ground attack pilot with 6. Staffel (6th squadron) of SG 2, Buchner was credited with 46 tanks destroyed. On 20 July 1944, Buchner was awarded the Knight's Cross of the Iron Cross. At the time, he had been credited with 46 aerial victories, including a Boeing B-17 bomber over Romania, and 46 tank destroyed, claimed in over 600 combat missions. The presentation was made by Oberst (Colonel) Alfred Druschel.
