no it's not. The "front bump" is an addon for scoping (obviously seen in Halo CE, ODST, and Reach). The iron sights are integrated and non-removable. If you've played/seen some Halo 2, the magunm has no "bump" because it literally is an attachment and wasn't in Halo 2.
nop
If you stare at the magnum long enough, it grows a scope.
But it dissappears if you live through the end of a game.
So, only the most dedicated of soldiers will have scoped magnums, because they're pro at staring.
In Halo 2 (and 3, I think) there was no scope on the magnum because the cheef was too busy pushing buttons and pulling triggers to stare at his magnum.