Justin, thank you. Sometimes disappointment can lead to progress. Look at this way, you've shown it can be done.
I will, look again, at different suppliers for a lightweight smoothbore barrel. It seems that the profile is the same for different bores, so larger bores are lighter. I ain't found a 50 cal. or 54 cal. thin wall smooth barrel yet.
What does a halfstock weigh, depending on the wood used? That gives an idea of the barrel weight desired.
I'm very grateful for the info that you've shared. It is an inspiring piece that you have.
I'm still crushed! Woodbutcher