I recently rediscovered a non-firing mgc68 mp40 that I'd had as a kid. At the time we didn't know what it was. I even showed my grandfather who had served in the US infantry during WWII who had used one when he was over in Germany. He said it felt right but couldn't explain why the barrel had no rifling or was plugged. Anyway I went into the Marines, college, got married had kids and forgot about it.
Last week found it was still at my parent's house and this time googled 'mgc68' to discover what it was. As I dig thru this forum even if I came up with a det pin, or suitable cartridge it seems very unlikely caps would be available in the United States except for perhaps ring caps for a toy cap pistol. I contacted Johnny V with plugfirecapguns in the UK who said currently with covid and brexit he's unable to ship to the US.
It is the early version with an uncut bolt face so at least it would be possible if the caps were available or there was a DIY cap method.