Continuity mistake: Ash has his shotgun stolen from him by the mini-Ashes who use to shoot at him. Ash then runs outside (all the while splitting into his good and bad halves) leaving his gun inside the windmill. Moments later Ash now has his shotgun again so he can blast Evil Ash in the face.
Trivia: The disbelieving clerk Ash is explaining his adventure to in the S-Mart ending is Ted Raimi, who can also be seen in the crowd below the castle battlements receiving Ash's pep-talk just before the battle with Bad Ash's Army of Darkness. Ted is director Sam Raimi's brother--and is best known for his part as Joxer in the Hercules and Xena TV shows (of which brother Sam was executive producer) where he again worked with Bruce Campbell.
Ash: Now listen up, you primitive screwheads. This... Is my BOOMstick! The 12-gauge double-barreled Remington. S-Mart's top of the line. You can find this in the sporting goods department. That's right, this sweet baby was made in Grand Rapids, Michigan. Retails for about $109.95. It's got a walnut stock, cobalt blue steel... And a hair trigger. That's right. Shop smart. Shop S-Mart. YOU GOT THAT?!