I think the reason that the boxes are marked like that is because semi-autos have a lower tolerance for longer ammo (longer overall case length = jambs in semis and in fact some pumps). The ratcheting action of a bolt action can actually seat the bullet farther into the throat of the gun, closer to the lands and grooves with a resultant increase in accuracy. Any benchrest shooter can explain this, I dont have the time to go into secant ogives on bullets and headspace/pressure issues. Suffice to say ammo marked like those should not be shot in a semi. In fact most "regular" factory ammo is designed to fit into virtually all guns of that specific chamber semis, pumps, levers, bolts. singles, etc. It might not be the most accurate ammo in the store but in reality a 1/2 inch at 100yds is meaningless when the shot is placed into bambi's boiler room.