As a pneumatically-powered airgun, primarily used for small game hunting or recreational target practice, the BB gun is with a base damage of only 4 the weakest gun in the game, even when boosted with the Cowboy perk. Thus it is largely useless against anything larger than a Radroach or Bloatfly. But then again, it is considered a silenced weapon.
The BB gun can fire a total of about 245 BBs, the equivalent of 2.5 reloads, from full condition before breaking.
With the Wild Wastelandtrait, the Abilene Kid gun will instead be located inside a well that appears in front of the shack. The well appears after talking to Rex upon him saying "aroo" and asking him if someone fell down a well. Doing this will cause the Courier to receive a map marker denoting the location of Jimmy's well.