Translation: the M4 barrel is so unreliable that special operations forces units need to swap it out with a barrel from a different gun -- and one that actually works in real combat conditions.

The improved rail will also have to include a low-profile gas block that could spell the end of the M16/M4 design’s traditional gas block and triangular fixed front sight,” the report says.

The improved rail will also have to include a low-profile gas block that could spell the end of the M16/M4 design’s traditional gas block and triangular fixed front sight,” the report says.