Unlike other officer and soldiers, First Lieutenant John McKay's (Dan Gauthier) sidearm is a blued Colt MK IV Series 80 with pearl grips. This is anachronistic for the time period of the series, as the MK IV Series 80 was first produced in 1983.
MGC M1911A1
Throughout the series, the MGC M1911A1 is seen in place of an actual M1911A1.
Tokarev TT-33
NVA officers and some other characters can be seen armed with the Tokarev TT-33 pistols.
Walther PPK Pistol
A Walther PPK appears to be the pistol seen in the hands of Lt. Beller at the end of "Three Cheers for the Orange, White and Blue" (S3E19).
Rifles
M16 Variants
The M16 rifle was the main rifle of the U.S. Army soldiers in Vietnam and is seen carried by most of the platoon. In the series, various models of the M16 are seen.
Colt XM177 (Colt Sporter Carbine)
A Colt Sporter Carbine modified to resemble the XM177 rifle is mainly seen being used by SFC Clayton "Zeke" Anderson (Terence Knox). For the remainder of the series, the Colt is loaded with the more accurate 20 round magazine.
The Norinco Type 56 is seen in the hands of the NVA and VC soldiers.
AKM
The AKM is also used by enemy forces as well as Lt. Goldman.
AKMS
In later episodes, Goldman carries an AKMS. In "War is a Contact Sport" (S3E18), an NVA tank gunner atop a T-55 is seen using one that's fitted with a drum magazine.
SKS rifle
The SKS rifle is seen a couple of times by NVA and VC soldiers.
SVD Dragunov
The SVD Dragunov is seen twice used by NVA snipers.
Submachine Guns
Smith & Wesson M76
The Smith & Wesson M76 is seen used by Pvt. Ruiz (Ramon Franco) on some SOG missions.
In 1966 the Swedish goverment blocked the sales of arms to the US as a protest against US involvement in the Vietnam conflict. As a result, Smith and Wesson created a clone of the Swedish M/45 which became known as the M76 on its release in 1967.
Carl Gustav M45
The Carl Gustav M/45 is used by Cpl. Danny Purcell (Tony Becker) and CIA Agent Duke Fontaine (Patrick Kilpatrick) on some SOG missions. The US forces in Vietnam used "deniable" weapons for some ops, which included the Carl Gustav.
The Ithaca 37 shotgun is seen in the hands of SFC Clayton "Zeke" Anderson (Terence Knox) in Season 3.
Machine Guns
M60
The M60 is the chief weapon carried by Pvt. Alberto Ruiz (Ramon Franco) in the series.
M60D
The "D" variant of the M60 is seen mounted on Huey helicopters as well as fired by enemy forces in the series.
Browning M2 HB
A Browning M2 .50 cal is seen mounted on US vehicles throughout the series.
Valmet M78
NVA forces are sometimes seen firing the Valmet M78.
Soviet SGM Goryunov
The Soviet Goryunov SGM Machine Gun or Chinese Type 57 machine gun is also seen used by NVA forces in the series. Actually it's not a real Goryunov machine gun. It's visually modified Browning M1919