Just for saftey's sake pick a ramp that is closest to the area that you want to fish, less travel time getting to the fishing area and more important, less travel time in case the weather goes sour. Most of the firing range outer cans are 6 to 7 miles out of one marina or the other. D-can for example would be about 6.5 miles out from Beef Creek and Niagra is about 7 miles out from Beef Creek with about 3/4 mile of that in the river itself. C-can would be closer to Wildwings or one of the marinas on Turtle Creek, A & B cans even closer, the inner cans J, K & L would be ok from any ramp located along the western edge of the firing range as long as it is not a high North or NE wind.
Pick your days and have fun, it is always better to have an error on the cautious side than on the risky side.