thanks for your welcoming!
Well, for the rules of safety I know them quite good. I test any new weapon I fear to be harmful since I have several larps here that allows big shots but want very soft weapons. I fear a tennis ball, even open, wouldn't be accepted, but I already have tested 2 types of projectiles. The first one's still the best, even though maybe I'm gonna put some extraweight with the sand, so it'll be heavy but have two steps of "rembourage" (Sorry, the english word skipped out of my mind)
P.S. sorry, the link you uploaded doesn't work outside USA
P.P.S. A friend of mine discovered that those "Stress balls" with happy faces on it are making great projectiles for Larps (He has a slingshot

) I tested it and it's turning out great.