150 is the closest you can shoot it, but that's cupcake shooting. I believe we can get 250 with Norm's Hercules.
Sorry to hear about the pile drivers, same kind of results I was seeing with the Rabbit Magnum ll. I tried the JSB Beast from the M10 out at 50 yards today, and came away disappointed with them as well. They open up and throw a zinger about every 5 shots in random directions. Peter may have been right about the spiraling. The JSB Monsters are not the cat's meow with the M10 either, but the H&N Baracudas will shoot one ragged hole at 50 yards so like you, I am back to them for my goto pellet for this gun. My P12 likes them as well, so maybe SPA barrels like the H&N pellets.