Man, you do find some great stuff. The above looks to me to be the exhaust for a Stuka. If, I wanted to have the eyes of knowledgeable metal detectorists see these, I'd post them @ http://www.treasurenet.com
"The MG131 (Shortened for Maschinengewehr 131 in German) is a German 13mm caliber machine gun developed in 1938 by Rheinmetall-Borsig and was produced from about 1940 to 1945. This Large-caliber MG-131 machine gun (13-mm) was the basic system consisting on arms of the German aircraft. The machine gun was widely used as synchronous, turret and wing." From.