So, for your base gun, how about something like...
Pistol
Superior one-handed ranged weapon
Cost: 25 gp
Damage 1d8
Proficiency +2
Range 20/40
Properties:
Load minor
Group:
Crossbow:
Firearm: When making an attack vs. AC with a firearm as a weapon, you can take a -2 to the attack and target Reflex instead.
Then you could have something else like
Rifle
Superior two-handed ranged weapon
Cost: 35 gp
Damage 1d10
Proficiency +3
Range 20/40
Properties:
Load minor
Group:
Crossbow:
Firearm: When making an attack vs. AC with a firearm as a weapon, you can take a -2 to the attack and target Reflex instead.
And because Jonah Hex will be in theatres soon...
[sblock=Pact Cannon]
PACT CANNON Level 2+
This dark steel firearm is the prized possession of any gun-toting warlock.
Levels 2, 7, 12, 17, 22, 27
Weapon: Firearm
Critical +1d6 damage per plus
Enhancement: Attack rolls and damage rolls
Property: If you are proficient with this weapon, it functions as a warlock implement (rod) for you (do not apply the proficiency bonus to attacks for implement powers).[/sblock]Finally, tackling the Training MC feat.
PISTOL TRAINING [multiclass pistol]
Tier: Heroic
Requirement: Con 13 or Dex 13
Benefit: You gain training with the pistol. You can make ranged attacks through your pistol without drawing opportunity attacks from threatening enemies.[sblock=Pistol Swap Feats]Pistol Novice [multiclass]
Requirement: 4th level, Pistol Training
Benefit: You can swap an encounter power of 3rd level or higher for the Crack Shot attack.
CRACK SHOT Feat Power
You scare the bejesus out of your enemy with the blast of your firearm.
Encounter * Weapon
Standard Action Ranged weapon
Requirement: You must be wielding a pistol
Target: One creature or object
Attack: Dexterity vs. Reflex. If you attack an unattended object, the attack automatically hits. If you attack an object wielded or held by a creature, target the creature's reflex.
Hit: 1[W] + Dexterity modifier damage and the target takes a -2 penalty to attacks until the end of your next turn (creature) or The target falls prone (object). If the target is an object, this means the creature holding it drops it and must retrieve it on the creature's next round.
Level 11: 2[W] + Dexterity modifier damage
Level 21: 3[W] + Dexterity modifier damage
Pistol Expert [multiclass]
Prerequisite: Pistol Training, 8th level
Benefit: You can swap one 6th level or higher utility power for the Revolver Action utility power.
Revolver Action Feat power
You've modified your pistol to shoot more often than others.
At-will * Weapon
Free Action Personal
Effect: You reload your pistol. Until the start of your next turn, any creature you attack with your pistol draws an opportunity attack from you if it moves during its turn without shifting at least 1 square first. Make these opportunity attacks with your pistol.
Pistol Specialist [multiclass]
Prerequisite: Pistol Training, 10th level
Benefit: You can swap one 9th level or higher daily attack for the quick and the dead attack power.
The Quick and the Dead [multiclass]
You know too well the cost of being a slow draw.
Daily * Weapon
Minor Action Ranged weapon
Requirement: You must be wielding a pistol.
Target: One creature
Attack: Dexterity vs. AC
Hit: 1[W] + Dexterity modifier damage, and ongoing 5 + Dexterity modifier damage (save ends).
Level 15: 2[W] + Dexterity modifier damage, and ongoing 10 + Dexterity modifier damage (save ends).
Level 25: 3[W] + Dexterity modifier damage, and ongoing 15 + Dexterity modifier damage (save ends).[/sblock]Rifle Training [multiclass rifle]
Prerequisite: Str or Dex 13
Benefit: You gain training in the rifle. You can make ranged weapon attacks through the rifle with your Strength modifier instead of Dexterity. In addition, rifles you wield have the high crit property.
[sblock=Rifle Swap Feats]Rifle Novice [multiclass]
Prerequisite: Rifle Training, 4th level
Benefit: You can swap a 3rd level or higher encounter attack for the Scatter Shot power.
Scatter Shot Feat Power
You throw a handful of rocks into your firearm and shoot.
Encounter * Weapon
Standard Action Close Blast 5
Requirement: You must be wielding a rifle
Target: Each creature in blast
Attack: Strength or Dexterity vs. AC
Hit: 2[W] damage and the target is slowed until the end of your next turn.
level 11: 3[W] damage
level 21: 4[W] damage
Rifle Expert [multiclass]
Prerequisite: Rifle Training, 8th level
Benefit: You can swap a 6th level or higher utility power for the steady shot power.
Steady Shot Feat Power
You brace yourself against the recoil of your weapon to fire with greater power.
At-Will * Weapon
Minor Action personal
Effect: Until the start of your next turn, add your Strength modifier to the damage you deal with attacks you make through your rifle.
Rifle Specialist [multiclass]
Prerequisite: Rifle Training, 10th level
Benefit: You can swap a 9th level or higher daily attack for the Blow'em away power.
Blow'em Away Feat Power
If they don't realize it's bad to be near you already, they soon will.
Daily * Reliable, Weapon
Standard Action Ranged 1
Requirement: You must be wielding a rifle
Target: One creature
Attack: Strength or Dexterity vs. AC, you do not draw an opportunity attack with this attack.
Hit: 3[W] + Strength or Dexterity modifier damage, and the target is pushed a number of squares equal to half your Strength modifier or Dexterity modifier and falls prone.
level 15: 4[W] + Strength or Dexterity modifier damage
level 25: 5[W] + Strength or Dexterity modifier damage[/sblock]
