Have measured wall thickness? I ask as you described "massive back bore," For safety sake you should verify if you have not already.
To answer your question, my guns minimum wall is around .060. French barrels are typically struck more robustly than other European guns, because, by law, French proof is the highest in Europe.
The chokes were opened on my gun, as well. There is also a pimple bulge in the left tube. WIth all that is wrong with it, the manufacturer inspected it, and figured it had more than a couple human lifetimes use left in it.
Best,
Ted
