I believe you have misunderstood the rule on page 6 under tools and weapons.
The +2 is not referring to +2 dice for a gun, but is instead referring to +2 for the success criteria. See Below.
Form Rule book:
If any of your dice rolls a 6, you get to say what happens to your Survivor. If none of your dice rolls a 6, the Narrator says what happens to your Survivor.
The Dangerous Survivor
The Dangerous Survivor has been trained with weapons. He’s a cop or a
soldier or just a gun nut. The Dangerous Survivor always rolls at least four
dice for any risk involving weapons.
A tool or weapon that gives you a +2 turns a 4, 5 into a 6, giving you a success
Hand weapons +1, Firearms +2
So a fast survivor with a gun, I would suggest a house rule that he gets to roll 1 die basic for using a gun. So he wants to get a 4,5,6 on a single die to Kill Zombies, as we all know you only roll dice if you are Killing Zombies.
In contrast a Dangerous survivor with a gun could be rolling 4 or more dice looking for success on 4,5, or 6 (or potentially successes) when killing zombies as this is using a weapon.