Here are the pictures of Yogi000's 4 bore Blunderbuss. Althought the muzzle looks pretty thin, it's spread. Now, it's either bores like that, meaning the true bore is thicker further back where it becomes a real 4 bore, or it's been swaged to that muzzle size and the barrel really is thin. Regardless, it is plenty strong enough for any load likely to be put through it. You'd need upwards of 450gr. of powder just to get pressures up to around 8,000PSi and that's unlikely, isn't it. The Big Bores truely are low pressure guns.
: Tks for sending me the pictures. I needed them for my file, Yogi!