I spend more time doing weapon research then playing CA these days, here my two cents on the issue:
* Shotgun spread does not change when moving OR jumping, unlike all the other weapons, so that why bunny-hoppers use them.
* They have a sharp cutoff distance of no-damage. In say Death Room, firing from half way in to the wall, will cause zero damage no matter how many rounds you fire.
* Shotguns IRL have very low penetration, so, for balance in a game IMHO, it would be *nice* if they became much more ineffective against heavy armour, but more against light armour, ie OHK at short distance for the lot.
* All shotguns should have the same damage (same shells), but Nexon chose different damage to balance the autos vs the pumps. A better idea would have been to force accuracy to be based on firing-from-hip and an aimed-down-the-barrel model, so then when you do get nailed you at least know the other player brought the weapon up, aimed and THEN killed you, rather then been in a mid-air jump, when all other weapons spray like crazy doing the same stunt. That way all shotguns could have dealt the same damage, and the variety of shoutguns could of had loading/times, aim time, swap time etc as the variables.