RE: how to install a 2nd sling post on sinthetic stock???
Most factory synthetic stocks have a strip of wood that the studs will screw into. If not you can get the Uncle Mikes installation kit and it will have all the information and tools needed to properly drill, counterbore, and install the stud.
If your rifle does not have the strip of wood you will need to get the machined screw studd with the collar that is glass bedded into the inside of the stock.