When Hardison fires the water balloon across to the other building, he aims straight at the target. The mass and air resistance of the water balloon would drastically slow it down. To hit the target, he would have to aim upwards at a 45 degree angle to arc the water balloon for the maximum range.
The ropes in the elevator shaft are obviously fiber. Real elevator cables are steel and very greasy.
When Sterling shoots the "body" and removes a piece of ballistics gel, it is not a blob but a perfectly cut cube. This would not happen unless it had been cut beforehand.