Ask the "expert" as to how many 300ultramags that "he" has shot until the accuracy went away.The accuracy life of a barrel depends on several factors such as how hot the shooter allows the barrel to get before letting it cool,how much pressure the loads are developing and the cleaning methods being used.As with any high powered rifle,rapid firing will cause barrel temperatures to rise quickly and will drastically shorten the life of the barrel.As such ,I shoot no more than three shots before letting the barrel cool.Using maximum or above maximum loads continually will also shorten the life of the barrel considerably.Lastly improper cleaning can shorten the life of the barrel.With these factors in mind the life of your 300ultramag could vary from as low as a few hundred rounds up to well over 1000 rounds.It will however be noticeably shorter than the smaller capacity cases such as the standard magnums or non magnums with the same usage and maintenance.