What sling was issued to the USMC with the M16A4?

What period of time? And what type of unit?

2006-2014 roughly, standard infantry nothing special.

From around 05 to 2010 the Marine Corps issued the 3 point, combat assault sling (NSN #8465-01-524-8847 ) which for most point was reviled by most people.  They also issued the standard black or OD green carrying strap to be used on the rifle range for table 1, which requires a loop sling.    Most people either bought their own or in the case of 2 MarDiv, they bought a BFG single point for every M4

In 2010, it was decided to start issuing the VCAS quick adjustable 2 point to infantry type units but you still see the 3 point CAS in non-ground units and some non-active duty armories.