
It's pretty good, but not the best.
This gun looks good, with 3 damage and +3, then it looks bad, with that and effect.
Another thing that's easy to miss, this thing is -ridiculously- cheap for a 3-shot weapon with a large bonus and 3 damage. You can easily play this in an asset heavy deck full of 3 cost assets (of which there is a lot in ) or some out of faction options.
That much damage and bonus is great, also the great price, but isn't the gun just completely kneecapped by that effect? Not quite.
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Old Hunting Rifle is a weapon the rewards a flexible playstyle combining and , ideally when the gun jams you evade and fix it, the missed shot can be recursed with cards like Oops! or Live and Learn so the gun does get good support from the faction. Will to Survive is nice but not always needed (although recommended if you intend to kill a boss). Edit: Eucatastrophe circumvents the autofails pretty beautifully.
The two stat reliance means that a classical combat specialist like William Yorick probably wont want one unless he's got all the support cards too (also Bandolier and Act of Desperation), characters like Silas Marsh and Rita Young however love them some Rifles.
One problem for 3 damage weapons is 4 health foes, in this instance it's good to have a high base and perhaps a Lucky! and/or skill cards handy to try and land a basic punch, Rita Young has a little advantage here thanks to her ability, which lets her simultaneously get distance to fix a broken rifle and damages the enemy.
"But random person on the internet," You might say, "dont Silas Marsh and Rita Young prefer Ornate Bow?!" Yes, the bow has more ammo in the end, and it might very well be more dependable, but the reliance on reloading seriously dampens what you can accomplish in a round, it's much easier to get the rifle to do 6 or 9 damage in a round. Rita in particular has no access to bonus actions outside Ace in the Hole and even that's just a one off, so despite her higher she actually might prefer the Old Hunting Rifle a bit. The big difference between the Rifle and Bow boils down to a lot of splitting hairs, the really fun thing is that you can take them both!
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Old Hunting Rifle isn't the best weapon in the game, it's risky, but it is very destructive and extremely cheap.