Likely is difference between what it WAS made as, versus what it IS now - a local acquaintance has a rifle stamped "30-06" on the barrel - but the belt recess in that chamber readily seen with the bolt open. A 300 Win Mag brass drops in, but a 300 Weatherby will not - I believe that a 338 Win Mag necked down to .30 caliber also "drops in" - so what is it?? Can not always believe what you read ...