Gunfighter at its finest
A model with gunfighter can make ranged attacks targeting models it is in melee with
If a model doesn't have a melee weapon it gains a melee range of 0.5"
An important thing to bear in mind is that it can make attacks on models "it is in melee with".
On page 43 of the rule book (I use the one included with war room) there is a section describing Engaged & Engaging
At the end of this section it states "When a model is either engaged or engaging, it is in melee"
Because gunfighter allows a model to make a ranged attack at models it is "in melee" with, you can make a ranged attack at a model with a 2" melee range even if your model with gunfighter only has a 0.5" melee range and the distance between the two models is 2".
There is an exception to this, however.
If a model with gunfighter charges, then it can only make its initial attacks on models in its melee range. Its first attack must be on its charge target.
If a model's first attack is with a gunfighter attack it doesn't count as a charge attack. This means it will not gain boosted damage as a result of charging - like a melee attack would.
Nor can it benefit from abilities like Runewood's "Path to Victory" which gives +2 to hit for charge attack rolls.
A cavalry model with gunfighter would not gain a boosted charge attack roll either, as gunfighter attacks are not considered "charge attacks".
So for example if Taryn charges this sword knight and kills it with her first attack she can't use her second initial attack as there are no more targets in her melee range (0.5" as she has no melee weapon).
If a model with gunfighter has the ability to buy or gain additional ranged attacks these are not limited to targeting models in its melee range after it charges.
So for example if Caine1 charges this Steelhead and kills it with his initial he can't use his second initial shot as he has no targets in his melee range but he can buy a ranged attack on any target in his guns' range, such as Damiano
If a model is engaged it can't gain the aiming bonus for forfeiting its movement - even if it is in a unit and is un-engaged by the time it makes its attack.
Missed range attacks while in melee
If a model with gunfighter misses an attack on a model that was in melee with more than one model, the shot must be re-rolled on one of them (randomising which model the shot might hit).
If the new model you roll to hit against is not in melee with the model with gunfighter then it will gain +4 DEF for the target being in melee.
Modifiers to ranged attacks
As a gunfighter attack is a ranged attack any modifiers to ranged attacks will apply to Gunfighter attacks
For example Caine1 is trying to shoot Damiano who will have concealment due to being in the forest. This also applies for terrain like Dense fog, or rubble - granting concealment and cover respectively.
If the target of a shot is on a hill but the model with Gunfighter is not on the hill then the +2 DEF for elevation would apply, likewise the same would be true with a trench template giving cover to the target if the attacking model is not in the trench.
Any special rule that prevents models from making ranged attacks would also apply to Gunfighter attacks.
As Gunfighter attacks are ranged attacks they would get around some defensive tech that a model might have, such as Set Defence or Duellist as these rules only apply to charge attacks (which Gunfighter attacks can never be) and melee attacks.
Models with spray weapons and the gunfighter special rule can make sprays while in melee but can only target models they are "in melee" with - although still roll on all models under the template.
A model with GF can make free strikes with its ranged weapon against a model that leaves its melee range. It gains +2 to hit and the damage roll will be boosted.
I hope this helped to clear up the rules surrounding Gunfighter for you.
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