Why would you want a semi in a magnum? Recoil will kick you off target so much that you won't come back for follow up fast enough. Precision is meh. 2 inch group, 1.5 maybe. You could do so much better for long range shots, and at close range its too much velocity anyway, 375 and 9.2 would be way better up close.
Plus you have a gas system to worry about. Automatics can jam, fail to feed, fail to extract and eject are more likely in an semi-auto. More parts, more springs, harder to clean and assemble. Just because it is auto loading the receiver is actually double the length compared to bolt action.
All for what? A 3 round magazine in a rifle you can't keep on target fast enough?
From the interwebs:
http://forums.benelliusa.com/archive/index.php/t-14472.html