Ok, i'll tell you which ones are good IB
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MP5 Navy - Excellent All Around, better for CQB (Close Quarter Battles). Tap the trigger and don't let it go auto.
P90 - Good, not as accurate as the MP5 but powerfull and packs alot of punch. Tap it as well.
AK-47 - I love this gun. If you tap and aim for the shoulders/chest you are sure to get a headshot from the recoil. TAP THIS MOFO!
Sig (T's) - Use the scope, push your mouse down if you are using the scope to fight against the recoil. Tap as well.
Colt M4A1 - This is the motherload. Great for Long range and CQB. I buy this even if I have $16,000. Tap it and you will own everyone.
AWM/AWP - Don't get me started, one shot kill..very cheap ass gun....
Those are the guns I like the best!