I don't think it's fatigue as much as the reduced recoil allowing a quicker second shot. And, quicker second shots result in higher scores -- bunker is a very fast game.The International community when the payloads were reduced from 28 to 24 grams, yet they found that the scores went UP as fatigue from recoil was less
Something not mentioned about bunker trap is the cost. Most ranges charge extra over conventional T & S fees. Also, you're going to use more ammo. Many bunker boys shoot twice at every target -- if they hit it with their first shot, they go for the largest chip with their second one. That equates to 50 shells per 25 targets.
Jim, my friend, that's because you're accustomed to entry level, multipurpose target guns. With higher grade comp guns, like Perazzi and Krieghoff, screw-in chokes are still an option. With a special purpose trap or Skeet gun, you may not change chokes. Why pay extra for something you don't need and that could be bothersome. And, there are those who may argue that fixed chokes work better.I can't think of a gun made today - by companies like Browning or Beretta - that do not have changeable screw in chokes
With the popularity of sporting clays and its frequent choke changes, the gun makers would have you believe they are required for all applications. Actually, they are reducing their client's options and increasing their profits.