When I was a member of NOBS, I made the mistake of answering that question.
My answer now is "It is all you imagine, and worse."
Please ask no further about it.
I would guess the UK analogue to my question would be "How many overnight shoots does a UK shot attend in a season?" Similar cost (per GOP), similar difficulties to attend (travel, room, what not)
I know I am using the Americanized version of "shoot" referring to clay target events, and my UK friends are more referring to "game shooting days".