I'm no expert at springing. . . i can only go a few inches (say eight) BUT, seeing as no real expert is helping, i might as well try to offer what advice i can
I found the biggest obstacle was: halfway through the cards began slipping off of my thumb, and springing downwards away from my other hand. It helped me immensely to concentrate on only allowing the cards to seperate from my fingertips.]
It might help to practice springing the cards "diagonally" with your pointer and mddle finger on one corner and your thumb on the other.
spring the cards both face up and face down when practicing. evens out the wear on them.
once you have it down, get a new set of cards. You'll be surprised at the difference.
My cards get hung up about ten from the end. solution? I simply close the spring as soon as i feel them stutter.
catch the cards in different ways. The way tought on the ellusionist video i learned from didnt help me at all...
Don't over bend the cards. relax the pressure nearer the end. sounds counter intuitive,m but try it for ten minutes or so.
start small. concentrate on aim. don;t think about distance until you can drop the cards into a near perfect stack from an inch or two up.
All of these tips were self-taught. voice of nights of practice. I'm sorry If i busted any copyrighted methods of teaching but if i did i did so inadvertantly
good luck