For your own safety and that of the people playing at your event you should if you haven't already very strongly consider looking into several ways of protecting:
2)The other players
3)The property owner
4)Other people who may be in the area who have no clue what you are doing there.
Quick youtube video
... because even though no one wants it to happen... sometimes shit happens.
The person it happens to may be your best friend and have no intention of making your life miserable, but if he happens to be the guy who falls off that 3 story roof or out a window and breaks his neck someone maybe not even him will decide to hold YOU and the property owner responsible hence the previous insurance question.
Second you are playing with "toys" which just so happen to look, by coincidence like a REAL firearm, and if a neighbour happens by chance across to where you are playing and sees one of your "toys" and thinks it is a real firearm or is shot and hurt or even shot and not hurt you have committed an offence with a firearm with the penalty just like using a real one.
Additionally if the police get called and told that their are a "bunch of guys with guns over yonder" they WILL show up and WILL treat it as if you are shooting real bullets.
There is plenty of info here on ASC if you go look for it from people have done what you are trying to do if you look it up and follow what needs to be done you will save yourself, and everyone else a lot of grief.