"This must not be a legaly registerd full auto MG-42 since it would cost over $25,000. So I am guessing it is a semi auto MG-42, either way it would use 7.92x57mm."
Not necessarily, he did state that the seller was a "friend" of his. For example, I could sell you my m11/9 for $1. If we are in the same state it's simply the matter of filing a form 4 ($200). If you're out of state, it's going to be $400. (form 4 - 3 - 3 -4). BTW, If you can find an mg-42 that is not a presample for $25k I'll buy it on the spot, sight unseen
"Of course this could also be a pre or post 86 dealer sample..."
It would be very embarrassing if a SOT didn't know the caliber of a mg-42. Even more so if it was a post sample - which doesn't make sense considering the vintage of the firearm.