I have an IAC Hawk 981R, it is a Norinco 870 clone. I am trying to install an aftermarket stock to it and cannot for the life of me get the stock bolt off with a flathead (it actually chipped the tip). Does anyone know what socket size it is? Or should I use a better flat head with a polygonal shaft so I can apply some torque with plyers? And will I run into any problems when installing the new stock? The bolt goes in through a pistol grip.