What are the strongest BBs to use?

It isn't the size of the BB that matters. Those guns aren't known for being very hard hitting. The gearbox inside of the rifles, which shoots the BBs is what matters. Go on airsoftgi.com or shortyusa.com and buy yourself a real rifle. anything 350 FPS+ will shoot a .2g-.25g very hard. the JG BAR 10 clocked in at 450 FPS with a .2g.