I recently bought a new synthetic stock for my sks. it sits a little loose inside. any ideas on how to snug the fit a little bit?

+1

Just guessing here, and it would be a little bit of a PITA, but you might fiberglass bed the action in the stock like you would a bolt gun.  That sucker wouldn't wiggle then and you'd never have to worry about it again.

If that's too fancy and precision shooting isn't your game (with a SKS?  haha) you might be able to use some silicon caulk to stabilize the action.  I've never tried it, but it might work (heard of a guy who did that to a 10/22 in an aftermarket stock with some success, but no experience personally).  Dunno.  Just a couple of ideas.

Shoe Goo, firmer than silicon.