A press photo of a US protective agent responding to a gunman breaching security during last weekend’s White House Correspondents’ Association dinner has ignited debate within America’s firearms community.

The controversy centres not on the agent’s actions, but on what appeared to be a Chinese-made Holosun red dot sight mounted on her Glock pistol.

The image, which spread rapidly across firearms forums after being shared on social media, shows a plain-clothes agent with her weapon drawn as US...