In reply to Ridge:
I regularly run through another piece of woodland in Flintshire that is used for airsoft, and at times the ground is littered with the tiny plastic pellets, there must be thousands left everytime they play. It is pretty amusing when they all have to stop due to the public footpath being used, it must break any immersion they feel in the game when a family of four, two dogs and a granny wander through.
Apparently you can buy biodegradable pellets, which seems like it should be enforced by the people running these things.