Most of the weapons in the game have a Vault Precious skin, but there are a select few that don't which just makes things feel... incomplete. (It would also be really nice if Vault crates couldn't give you something currently in your inventory unless you have it all, but I digress...) Probably a low priority development wise, but the following weapons could use Vault Precious skins:
Standard:
M99
Goreshiv
DLC: (Note that some DLC weapons do have Vault Precious skins, like the Rhino)
Minigun
Frost Fang
Blunderbuss
Mine Reconstructor
Glock 18C
Mosin Nagant
Compound Bow
Riot Shield & Glock 18
And obviously none of the HRG weapons have Vault Precious skins, but I expect that's intentional and I'm perfectly fine with that.
Standard:
M99
Goreshiv
DLC: (Note that some DLC weapons do have Vault Precious skins, like the Rhino)
Minigun
Frost Fang
Blunderbuss
Mine Reconstructor
Glock 18C
Mosin Nagant
Compound Bow
Riot Shield & Glock 18
And obviously none of the HRG weapons have Vault Precious skins, but I expect that's intentional and I'm perfectly fine with that.