Magnums have some long throats. Just the way it is. It to keep that initial pressure spike down. You think that is bad, my 300RUM had 3.82" with 180gr barnes bullets to the rifling. But its hard to find a bullet you can load that long and factory data was normally 3.58".

You'll find much shorter throats in your 308's and 30-06s. The most important thing is your not in the rifling and you can fit the loaded round in your mag.