I like to use a 7/8" forstner bit to drill the holes. It just small enough that the socket can't come out.
I then dish each hole with a large cove bit in a router.  This accommodates the shoulder of the bulb.
The hole is too small to use a bit with a bearing, so I just plunge each hole. A 3/4" hole will work,
but I've had bulbs with larger shoulders than others and it's a very tight fit, breaking some of the bulbs in the process.

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