simon6ppc,
I have been an avid PD shooter for well over 50 years and have had access to some of the best towns in the west and I will have to say that 500 round PD shooting days are like the "half-inch group all day long", there are more of them on the internet than in actuality. Last year my shooting partner and I were in a completely virgin town that had never been shot before, at the end of the day between the two of us we had shot just over 600 rounds (total, not each), using multiple rifles, this is an above average day in my years of shooting.
As far as a 1200 round day - it just doesn't pencil out. Figuring a 12 hour day without taking a break that is a hundred rounds per hour, or a round about every 40 seconds. Now that would be not leave much time for a break to drink, eat, or clean a rifle, and darned little time to load magazines, change rifles, or relocate to a different part of the town as the dogs start to become gun-shy. That is not factoring in the eye strain and sore shoulder one would have, even using a light recoiling caliber like a 223. In other words a person would have to start shooting at somewhere around 6 a.m. and shoot a shot every 40 seconds without a break until 6 p.m. that night. I am not sure that is humanly possible, sometimes things are bigger when remembered than they were in actuality.
In my years of shooting and of those I know who have shot PDs for many years a good day is somewhere around 200 to 250 shots a day. I have seen very few towns anywhere that will support much more shooting than that. So don't be too envious when you hear tales of near unlimited shooting.
drover