I think 18% is an extremely hard stat to reach after 120 sorties or so, and I challenge any of these weenies to try to do it next tour and post it in this thread. Again, it is nearly impossible without great amounts of extreme dweebery. 
It's not as impossible as you think, it really just takes some discipline to get a high hit percentage without having to resort "dweebery" to achieve it.
1) Fire within close ranges (400 yards or closer)
2) Do not strafe anything (i.e. GVs, buildings, vulching)
3) Do not take high probability snap-shots, only take shots that you know will land.
4) *Most Important* Learn how to aim with your piper instead of your tracers
Even with those four simple rules, one can easily achieve an 18% hit percentage if one has the discipline to go for it. YMMV.
ack-ack