For whatever reason, the sawed off grip included with the NT-79 has a lug inlet of 27.2mm, while the receiver lugs are 28.2mm. Print this part so you do not have to hand fit. QD cup integrated into base of grip as well.
From the Tinkercad vault
LBRY Tags: nt79; 37mm; launcher; fosscad; 2a3d
** DEPRECIATED ** 37mm High-Efficiency Rupturing Base Signal Rounds
HAVOC 12 inch 37MM Launcher stand alone stock adapter