Buy a train ticket from Abilene to either San Francisco or Pittsburgh, then board the train. You'll notice a container containing 'an assortment of weapons', but attempting to get a weapon from the rack immediately wil not result in anything happening. After the train sets out, there'll be a message that the conductor has sighted buffalo. At that point, GET WEAPON RACK and hold it (it can have varying descriptions). Shortly after the warning, everyone in the train car will start shooting at the buffalo. There will be three opportunities for you to SHOOT BUFFALO (you don't need any sort of gunplay skill, or even to be from a town that can learn to use guns in order to do this quest). You have a short window to shoot buffalo after you are informed that you have a shot, but the results seem to be pretty random (even on a 100 perc shooter).
Eventually the event will end, the train will stop, and there will be a room to your north containing a buffalo skull, if you shot one or more buffalo successfully during the event.
If you shot all three buffalo, you will be awarded this whois. Good luck!