A stuffing trick

Getting your projectiles stuffed tight enough can be difficult.  Often, it comes down to you jamming one bean at a time into the last stitching hole before you close.  But here's a trick.  Twist stitch the last two inches or so a bit loose, then stuff the ball tight as usual.  Right before the final closing knots you can go back and pull both sides of the twist-stitch tight.  This will give you a bit more slack for the closing knots and pull the halves together giving you a nice solid ball to sling with.