erik grant (originally made the ironsight system for insurgency) actually suggested they not use it in neotokyo. Mainly due to the a lot of limitations the source engine currently has on bobbing, movement, and freeplay on the gun WHILE shooting causing severe inaccuracies that should not be present.
If you play Insurgency, or know anyone that plays its often. You'll notice, or they will probably say the iron sights in the game range from slightly, to wayyyyy off. Especially with the M16/etc. While a lot of new players getting used to the game might think this is purposely intended, its actually a problem they can't fix.
While it is nice to have a short realism affect on shot in real life (causing temporary blind spots around the iron sight in certain distances). I can see why they really want to try to avoid it to focus on other things that severely need to be adjusted.
To be honest, with as much smack as I've heard in the past from the developers over how much they hate the source engine. I'm surprised they are still moving with it. (But I guess it sure beats the neotokyo mod they tried with UT2K4 by a million miles).
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