Need some of the sticky backed (soft side) velcro, take off stock, stick ~1inch square inside where the buffer tube goes (on the top edge), stock back on. Wobble solved.
Yeah, I wasn't greatly impressed with the fit of my magpul parts, even the foregrip required some modification to fit.
Probably more down to the tolerances of your gun Adam. Magpul can't make loads of versions to fit all makes, G&p takes them well.