I'm not real sure, but if I'm not mistaking I believe a shot of whiskey costs the same amount as one cartridge. Cowboys in saloons would trade one cartridge for one shot of whiskey. Thats where the term "shot" of whiskey comes from.
Neemo: So if you want these horses, I sell them to you. Did you bring some gold with you? John Chisum No. Neemo: Silver?
John Chisum: Just lead!