In basic mechanics, both the Standard and Tactical S&W M&P15 versions are typical-format gas-operated semiautomatic .223/5.56mm AR-15A2-type designs. Both feature 16-inch barrels with chrome-lined bore, chamber, bolt carrier and gas key. The flash suppressor on both is the A2 military style.
The Steyr Scout is a modern bolt action scoped rifle produced and manufactured by Steyr Mannlicher and primarily chambered for 7.62 mm NATO (.308 Winchester). The weapon however is also offered with other chambers commercially. The Sniper Rifle is often called the Mannlicher Scout to reflect the company's alternate name.
The SOF Combat Assault Rifle, or SCAR, is made by Fabrique Nationale (FN) for the elite U.S. Special Operations Command (SOCOM). The SCAR is a modular rifle made to satisfy the unique and specific requirements of the SCAR competition.