This is want I think you want to know. I own a SBE I and a Extrema II. The SBE I has problems
in dirt Goose pits with alot of dirt getting into the action. This is well known thru out our hunting club of 200 members. I have not had that problem with the Extrema II. The SBE I will not shoot light 1oz loads unless you install a lighter recoil spring. The Extrema II will. The Extrema is harder to clean, but the Extrema has much less recoil with heavy 3 1/2" loads. Assuming a clean gun, most of my jams have been from improper sized ammo. I had some Federal 3 1/2" BBB steel shot that would not operate through either gun, it had to be those loads.
Not every round in the four boxes was bad, but after I checked them, there will many that were oversized.