The stuff i use is an even mix of sharp sand and then every size up to small (say 30mm) stones.
They key bit it all fits together to make a solid mass with no gaps.
Some images here:
If it was delivered in a bag tip the bag out on to a board and turn it over with a spade a few times to distribute the stones around. This will give you a better idea how many stones there are. Sometimes they settle in storage though vibrating the load will tend to lift them to the surface. (The sand settles down into the small crevices and get under the stones thereby lifting them up).
Plenty of stones in there.
My stuff from BnQ