Does proficiency with the hand crossbow grant proficiency with this rare weapon?

Question

+1 keen dart gun (9,300 gp; treat as a hand crossbow that automatically reloads itself, stores up to 20 darts, and allows its wielder to fire an additional shot per round as if using the Rapid Shot feat. This is an exotic weapon.)

So, yeah. My plan is to play a hand-crossbow focused character through the series of adventures that ends with you acquiring one of these babies. The ending "This is an exotic weapon." makes me wonder, though, if the weapon is intended to be a separate proficiency, such that Hand Crossbow proficiency wouldn't be enough. Will I need to spend a feat on Exotic Weapon Proficiency (dart gun), or will being Hand Crossbow proficient be enough?

While I didn't tag this as Society specific (because the answer shouldn't be different), if it does matter, this is for a PFS character.

Answer 1

Yes, proficiency in hand crossbow allows you to use this weapon.

The hand crossbow is an exotic weapon. The description of this weapon says "treat as a hand crossbow that {does things}." The description also says, "This is an exotic weapon." The weapon description says to treat it as a hand crossbow that has special properties. This would be no different from treating a special longsword that has special properties as a longsword. Therefore, proficiency in hand crossbows (or exotic weapons) is required to use this weapon.

Answer 2

As originally presented, this dart gun is probably different from the hand crossbow, but that's an unlikely ruling in casual play

Some similar dart guns appear in The Emerald Spire Superdungeon.¹ Here, from that adventure, is the original description:

The dart gun functions as a hand crossbow that can hold 20 darts and automatically reloads between shots, allowing the wielder to make full attacks with it. It fires an additional shot each round as if its wielder possessed the Rapid Shot feat. A +2 keen dart gun is worth 9,3000 gp, [sic] and is an exotic weapon that [adversaries that wield them] are proficient with. (145-6)

Because this weapon only functions as (that is, compared to is treated as) a hand crossbow, it has a hand crossbow's statistics except as presented in the text, and the text calls the weapon a different name, so it's not a hand crossbow. There's no indication that the proficiencies are equivalent like, for example, composite longbows and longbows. Additional evidence is in the adversary's stat block: the creatures have Weapon Focus (dart gun), not Weapon Focus (hand crossbow), which, were the latter feat present, would've conclusively expanded the hand crossbow's mandate to the dart gun.

I would totally agree with this answer that the feat Exotic Weapon Proficiency (hand crossbow) would be sufficient to avoid a nonproficiency penalty for the dart gun if that description did say treat as a hand crossbow. Further, were I GMing The Emerald Spire Superdungeon for a PC possessing the feat Exotic Weapon Proficiency (hand crossbow) and that PC acquired one (or more!) of these weapons, that description would be close enough for me to let the PC use it without suffering the nonproficiency penalty. But, if the GM's taking an ultra-strict, rules-as-written, take-no-prisoners, you-get-a-trophy-for-winning position, then, according to the text, the dart gun and hand crossbow are probably different weapons and don't share the hand crossbow proficiency.

Finally, the above dart gun is decidedly different from the typical Pathfinder technological dart gun that requires, instead, the feat Exotic Weapon Proficiency (firearms).

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¹ I am unaware of other published +1 keen dart guns in Pathfinder products. If +1 keen dart guns appear in other adventures with descriptions matching those of the question, I happily defer to this answer.