I've dug with a gun my entire life and I always dig with my back to the ocean. The angle though depends upon the beach you're digging. On some beaches, clams will lay differently than others and you have to adjust. I've found places where I actually have to place my gun behind the hole entirely.

Some hints ... go down slow, and get yourself a custom gun ... We've had them made with 5" tubes rather than 3" and very, very rarely ever break a clam ... even when digging hundreds over the course of a tide series up north.