Ok let's have a think..erm SWAT 3 is good. Project IGI very good and pretty hard- damn good weapons and weapon animations.
Counter-Strike for Half-Life.
Firearms for Half-Life.
Sven-Co-Op for Half-Life isn't really military and realistic but play it with friends and it's damn fun.
And Serious Sam- one hell of a fun game so funny and the weapons are funny. It's like Doom but better.

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Caparzo