An AR-15 or a Mil/LE M4 modified to use P90 magazines and shoot the 5.7x28mm bullet. The AR-57's shells eject from the magwell and it also has no gas system. It's available in three types, 16.04" barrel, SBR 12" barrel, and internally suppressed 12" barrel. It's very reliable and very accurate.
by qwdhjcadsvhbcwekrbvwue August 16, 2013