@Arturia
That would be the M-14. It's long barrel make it look sexy. It's the full automatic version of M1 Garand, but using 7.62x51mm NATO ammunition instead of .30-60 Cal.
Look at her, ain't she a beauty?
But since you said, modern weapon, I'll goes for it's modern version, the M-21. The different between M-14 and M-21 is that instead of having the full-automatic firing mode capability like M-14, the M-21 only have semi-automatic firing mode.
@Shitotaku
Yes, I have re-watched several animes like SDF Macross, OrenoImotou, Azumanga Daioh, Mospeada, Suzumiya Haruhi and more.
Have you ever download a complete series of anime but never watch it yet after all those years/months?
I have, plenty of them still sitting in my HDD, unwatched.