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Excerpt: On this day in 1981, President Ronald Reagan was shot in the chest at the side entrance of the Washington Hilton on Connecticut Avenue by John Hinckley Jr. Reagan was walking to his limousine after a speech to AFL-CIO leaders when Hinckley, 25, who was standing among a group of reporters, fired six shots, hitting Reagan and three others.
While it would be difficult to know exactly everything they have, they seem to have kept up with the times. The Uzis have been reportedly phased out.
In recent use, the secret service definitely has Knight’s Armament Company 5.56x45mm SR-16E3 CQB rifles.
MP5A3s (possibly MP5A5s, but MP5A3s seem more overall popular with law enforcement, and full auto seems more like what USSS would choose.). I've never seen MP5Ks in USSS hands, but I wouldn't be surprised to learn about them.
P90s.
Remington 870 PGO shotguns. Probably intended for breaching, but possibly for less-than-lethal rounds. The USSS agent in the photo is carrying 5.56mm magazines, making the shotgun clearly not the primary long weapon.
While I've never seen an MP7 in USSS hands, a solicitation request from 2016 seems like it would be a good fit for them.