It wasn't about building a shitkicker rifle though, just using a casing that was easy to get and plentiful. Also making it a bit milder to shoot and the mag will feed after a minor mod of the front lips.
.307 Winchester is actually a bit more than I'd want to put through a .303. More like .308 and without a new action I'd be wary of stretching the action. Even if you reload the time may come when the rifle goes elsewhere and someone will slip a factory round in...