Barrels do not wear out but rather erode from pressure and temperature(sort of like flame cutting with a torch)in the throat area just ahead of the chamber.The hotter you let the barrel get the faster it erodes.If you do not let the barrel heat up(shoot three shot groups and let the barrel cool) you should expect peak accuracy for about 1500 rounds with this type of cartridge.My 7mmstw's both shoot 140 gr bullets at right around 3500 fps and provide 1/2" groups while doing it.