The Polish 7,92x107mm was good for a few hundred rounds in the barrel, same for the German 7,92x94mm.
my photos show making the 7,92x94mm dummy from aluminum, once you get the dimensions, just takes a little time.
other photo shows 7,92x57, 7,92x94, 50 cal US (1933) and 55 BoysAttachment 121008Attachment 121007Attachment 121009