Less Basic

The basic load I mentioned earlier did not mention accessories or optics.

The "standard" M4 will be getting what used to be called the SOCOM barrel and getting full-auto instead of three round burst; so they'll all be M4A1 SOCOM now.

13.8 lb. with 210 rounds.  Bare.  No sights, no optics.

An Aimpoint CompM4 (aka M68 CCO, not to be confused with the M68 CCO) adds 0.75 lb.
A Matech folding rear sight adds 0.18 lb.
Changing the handguard to a Knight's RAS adds 0.15 lb.
An AN/PEQ-16 adds 0.62 lb.
A couple of Knight's rail covers for the sides; 0.12 lb.
A Gri-Pod vertical grip; 0.44 lb.
Silent sling; 0.3 lb.

So we've added 2.56 lb. to the mess.

16.06 pounds for the weapon and ammo.

The Marines have it a little worse with their M16A4; 15.4 lb. with ammo and detachable carry handle (0.6 lb.) before we start accessorizing.

Their RAS is 0.3 heavier than the stock handguards because it's longer.
They use the Knights 600m micro rear sight for a BUIS when they issue one. 0.09 lb (replaces the handle for a net -0.51 lb.).
They issue the Trijicon ACOG TA31RCO (AN/PVQ-31) 0.62 lb. instead of the Aimpoint.
They also throw more rail covers at the problem. 0.27 lb.
An AN/PEQ-16 adds 0.62 lb.
A Gri-Pod vertical grip; 0.44 lb.
Silent sling; 0.3 lb.
2.04 lbs added to the gun overall.

17.44 lb.!  And if they decide to pocket the detachable carry handle instead of mounting the BUIS it's back to 17.95 lb. all up.  That's right back to where the M14 was in Vietnam (including 0.4 lb. M1 sling).

Update:  I forgot, to be able to USE that AN/PEQ-16 you're going to be needing a pound of AN/PVS-14 to see the IR laser.