DALLAS - Relatives of legendary sharpshooter Annie Oakley are offering a collection of items - including her Stetson hat, guns, letters, and photographs - in an auction that one expert says hits the mark for its breadth and sentimental value.

On Sunday, Heritage Auctions will offer about 100 Oakley-related items in Dallas, including a 12-gauge Parker Brothers shotgun expected to bring about $100,000. Two Marlin .22 caliber rifles are expected to sell for more than $20,000 each.

Oakley gained fame in the 1880s and 1890s for her shooting skills as a performer in Buffalo Bill’s Wild West show. She died in 1926 at 66 but has remained a pop culture icon.

“The country kind of took her to heart,’’ said Tom Slater, Heritage chief of Americana auctions.

Over the decades, her likeness has appeared on everything from dolls to lunchboxes and her story led to Hollywood films and Broadway’s “Annie Get Your Gun.’’

“She was just sparkling as a public performer,’’ said Paul Fees, former senior curator at the Buffalo Bill Historical Center in Cody, Wyo., with whom Heritage consulted on the auction. “This petite person handling firearms was startling. She was a natural at it. She made it look easy.’’

The items are being offered by Oakley’s great-grandnieces - sisters Tommye Tait and Terrye Holcomb of California. They inherited the items from their mother, Billie Butler Serene, who died in 2009 at the age of 95.

Serene was raised by her grandparents, and her grandfather, William Butler, was the brother of Oakley’s husband, Frank Butler, a marksman who was Oakley’s manager. Oakley and Frank Butler frequently visited and Oakley taught Serene how to handle a gun.

Holcomb said that she had grown up with many of the items, such as Oakley’s famous Stetson with a ribbon trim - expected to sell for more than $4,000 - which was a favorite for school plays and Halloween costumes.

But Holcomb and her sister did not realize how many of Oakley’s possessions their mother had until they went through the West Los Angeles house after her death.

Fees said several museums across the country have collections related to Oakley, including the Garst Museum’s Annie Oakley Center in her hometown of Greenville, Ohio, and the Buffalo Bill Historical Center.