“We are locked in a struggle with powerful forces in this country who will do anything to destroy the Second Amendment,” said Richard Venola, a former editor of Guns & Ammo. “The time for ceding some rational points is gone.”

There have been other cases like Mr. Metcalf’s. In 2012, Jerry Tsai, the editor of Recoil magazine, wrote that the Heckler & Koch MP7A1 gun, designed for law enforcement, was “unavailable to civilians and for good reason.” He was pressured to step down, and despite apologizing, has not written since. In 2007, Jim Zumbo, by then the author of 23 hunting books, wrote a blog post for Outdoor Life’s website suggesting that military-style rifles were “terrorist” weapons, best avoided by hunters. His writing, television and endorsement deals were quickly put on hiatus.

Garry James, a senior editor at Guns & Ammo, said in a phone interview several weeks ago that its readers were the magazine’s main concern and its editorial independence was not at risk. But, he added, “advertisers obviously always have power, and you always feel some pressure.” He declined to discuss Mr. Metcalf’s matter specifically, and the company did not respond to further phone calls and emails seeking comment on other aspects of the operation.

Mr. Metcalf said he was told that advertisers feared customers would boycott their products if they continued to advertise on TV shows and magazines featuring his work.