Most skirmish quality ammo (BBs) is similar but you must always use skirmish quality ammo that can be bought from airsoft sites and shops. Sometime you can find cheap ammo in supermarkets and high street shops, but you should never use this as it will almost certainly jam in the barrel of a good quality replica, and can cause damage as a result. Some brands of skirmish quality ammo will still give erratic flight paths and some brands do not feed from magazines very well, but if you ask your fellow players you will soon find out which good brands are available and cheap at the moment (it changes year by year). You can always buy ammo on site but will be more expensive than if you buy it in bulk from a shop. Never ever reuse ammo that has been fired already; even if it looks undamaged it will have internal cracks and is likely to break apart in your replica when you try and fire it. Different weights of ammo are available but stick with 0.20g or 0.25g BBs; heavier ammo doesn’t really help you when using stock replicas at UK power limits. Airsoft BBs are available in anything from 0.12g to 0.50g.
6mm is the industry standard but a handful of 8mm replicas exist. AEG’s are almost always 6mm but may be advertised with 7mm and 8mm gearboxes. This is the size of the gear axle bearings and not the ammunition used.