I also use machine screws and nuts, short ones, 10x32 x 1/2" i think they are
nuts get epoxy bedded inside.
here's how i do mine
lightly grease the screw only and do not grease on the outside of the nut. install the screws and nuts and then use an epoxy putty to cover the nuts. the lightly greased screws will remain removeable. or skip the grease for a permanent mount.
then install your action and be sure the oprod/gas assembly are properly clearanced from the nuts/epoxy.
or mess around with rivets hehehe