when shooting from a bench, the 338 winmag is about my limit as well. Anything below and i can keep my groups small and clean. anything above and they open up a bit after a few shots. I dont notice myself flenching, tightening up, getting sloppy with my breathing, or anything like that with larger rounds, but for some reason my groups tend to open up with anything larger than the 338 wm and I havent figured out why yet, so its my limit for now.