I like coldfire's gun. Nicely done and well thought out, however, the 6.8mm calibre is hardly ever used. Hate to be pciky, but a more realistic calibre would be 5.56 or 7.62.
I chose the 6.8mm as a compromise, actually. In my experience the traditional 7.62mm round provides good stopping power but has too much recoil, making it difficult to use full-auto. The standard 5.56mm NATO round is far easier to manage recoil but isn't nearly as potent as a 7.62. The 6.8mm provides a balance between stopping power and recoil that makes it good for medium- and close-range work.
If I were going to make a 7.62mm weapon, I'd make it a long- to medium-range weapon ment to be fired semi-auto most of the time. The M7c design that I posted was a carbine, ment for special forces CQB situations. The M7c is a bit like the M4A1, and like the M4A1 has the M16, the M7c has a larger cousin.
Presenting the M70 assault rifle.
(Yes I did get the external look by crossing a XM8 with a F2000
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