while not universally true, a good tip for new diggers- I find the clams are not as deep and show much better early in the tide cycle, when the low is not that long after sunrise. After several days of the beach above them being exposed and dry, many of the razors seem to stay deep and wait for there to be more water above.
last Monday, 6am low, the first day of this cycle- big shows all over, I was done in 20 minutes and the clams were mostly just half the gun deep.
then on Sunday, same exact beach, 11am low, last day of the cycle- very subtle shows, some just a small disturbance of wet sand as a wave receded, took me 2 hours to limit and most were at least a full gun deep, several took a second punch to get.