“In photographs of the Secret Service snipers, they appeared to be using long-range and powerful rifles that likely fire .300 or .338 cartridges, commonly used by well-trained military snipers.”
https://www.nytimes.com/2024/07/14/us/politics/secret-service-snipers-trump-rally.html
(I would not rely on NYT for any firearm info)
What Weapons do the Secret Service Use? [2022 Guide]
https://reloadyourgear.com/secret-service-weapons/
Thanks; good links.