I'm no expert but when I used to run a shooting sideshow at our MAG Biker rallies, we used Gat pistols with corks to knock coloured wooden rings over the necks of bottles to win prizes. We found that the harder you pushed the cork into the end, the better seal you got and the cork was double in velocity over one that was loosely fitted, so I don't think inertia was the driving force, I think it was air....could be way off target though, like the corks always were!!