Heckler and Koch began work on the OICW platform in the late 20th century that eventually berth the XM8/XM8A1 weapon that we see in-game. Across both installment it's in, it bears average stats all-round. As far as assault rifles go, this one most closely embraces the "Jack-of-all-trades, master of none" cliché.
Strike Force Heroes 2
The XM8 is an Assault Rifle usable by the Engineer. Stat wise, it is rather painfully average, with okay stats all across the board.
Strike Force Heroes 3
The XM8A1 is a fully automatic balanced assault rifle. It is unlocked by completing mission 17 on any difficulty.