The M16 FOW ( Family of Weapons of which Diemaco's C7/C8's are included) are of direct gas design, similar to that used on the 6.5 x 55mm Swedish M-AG-42-B which as been around since the early 1940s.
Blowback is simply that. The force of recoil drives theh bolt/action back. This is common for open bolt firing weapons, such as 9mm SMGs like the UZI, STEN, PPSH-41 (7.62 x 25mm), MP40, and the C1 Sterling. There are countless others.These types of weapons are simple in design and easily mass produced.
The HK family (G3, PSG-1, HK33, MP5 etc, plus the unique French FAMAS G2), are delayed blowback, closed bolt firing. Along with the recoil, flutes on the walls of the chamber are utilised to have hot gasses pass by, and strike the face of the bolt to drive it to the rear.
The FN C1, M1 carbine, M1 rifle, M14, SKS carbine, and AK family are all gas operated incorperating a gas piston. Even modern assault rifles like the F88 (AUG) Austeyr, SAR-21 and FNC are all this way too.
MGs such as BREN, M60, MAG 58, Minimi, and the Soviet PKM family, and 12.7 x108mm DSHK's also use pistons in their gas system. While the Maxims (MG08, Vickers, etc), German MG34/42, MG3, US M1919A4's are recoil operated with gas boosters on the muzzle ( no piston). The Browning .50 (12.7 x 99mm) in M2HB and QCB configuration are recouil operated with no gas booster.
Don't wanna confuse ya.
Wanna know more? Do a search for blowback, delayed blowback, and gas operated.
Regards,
Wes