Anyone considered using infra red lasers as ammunition instead of bbs? There's a system that's out in the USA that has been designed for paintball but would adapt quite well to airsoft. It's like the military Miles system.
Some milsim paintballers have tested it with good results. Engagement distances up to 450 metres! You get a barrel (I'm currently designing a unit based on an AN-PEQ2 battery box) and a sensor for £80 inc p+p, extra sensors are about £15 each.
I'm planning on designing frag grenades and claymores eventually.
http://uk.youtube.com/watch?v=dBUSJjv262MAny comments? Anyone interested?