Heroes may fire ranged weapons when engaged in melee with a few caveats:
The attacker may only use a power or a one-handed ranged weapon (such as a firearm no larger than a pistol) when in melee. He may not fire rifles or other “long arms.” The TN is the defender’s Parry instead of Short Range as he struggles, wrestles back and forth, etc.
If attacking a non-adjacent target with a ranged attack while in melee, the attacker instantly becomes Vulnerable.