While it is true the .410 will run to higher pressures than the larger gauges, it is also true that upon firing this higher pressure is within the chamber area. At this point I would think the adapter itself is capable of holding the pressure. As soon as the adapter is cleared & the load enters the much larger bore area of the carrier gun pressures are going to drop significantly. The bore area of a .410 is only about 38% of even a 20ga. My 16ga Savage Four-Tenner is 12" long. By that point & coupled with the large increase of bore area, if the bbl won't hold it I would fear to stick a cork in the muzzle & blow hard on the breech.
