In my case, I won't use anything but Bastards or Madbull Precision (non-Bio). They're the only ones that haven't caused either jams or damages to my guns. While I haven't tried Bio Bastards, I've never used another brand of bio BB that hasn't caused issues or damage. I simply refuse to use ammo that will potentially damage my guns. You'll find many airsofters in the same situation. Unlike paintball, by restricting ammo type, you also restrict your client base significantly when it comes to airsoft.
Honestly, if that's what I was being forced to use to play at a certain field, I simply wouldn't play at that field (it happens more often than you may think). I value the high dollar investment I have in my guns far more than a new venue to play at. You'll find the expensive "field ammo" model that's been the mainstay of sucking money out of paintballers is not a model that works or is accepted by the airsoft community. You're better off charging higher field fees and letting people bring their own ammo they're comfortable using.
If you insist on bio BBs, then make that a stipulation. Perhaps have some quality bio BBs (like Bastards) available on field at normal (not inflated) prices for people that don't have any. Then you can be a retailer for a known and trusted brand and not have to worry about policing people for "field BBs only".
Personally this doesn't affect me. I'm out of your area and the likelihood I'll ever play on your field is slim to nil. But I support the growing sport, and I'm glad to see more paintball fields getting in on the growing popularity of airsoft. But keep in mind that this is already a well-established sport with standards and practices already in place. If you try to force the "paintball model" on people because of your own inexperience with airsoft (trust us, they're 2 very different animals with a very different clientele), things probably won't work out as well as they could.
I wish you the best of luck and hope you can prosper while bringing London-area players a new venue to play at.
Last edited by Crunchmeister; May 24th, 2012 at 10:58..