This was a commercially-published supplement. It's currently available on DriveThruRPG. It contains stats for the following weapons (which will not be posted on this wiki), as well as modular rules for constructing virtually any possible AR-15 variant.
ArmaLite AR-10A4 and AR-10(T)
M16A1, M16A2, M16A3, and M16A4
M4, M4A1
Diemaco C7, C7A1, and C7A2
M231 Firing Port Weapon
Colt RO635 and 639
Mk 18 Mod 0 CQBR
Olympic Arms OA-93
AMU National Match Rifle
M110 SASS and Mk 11 Mod 0
SAM-R
Heckler & Koch HK416