On some bows, you can actually feel the stretch in B-50 when you're drawing the bow. One bow I had, I swear I could pull the string nearly 3" before getting much movement in the limb tips. I had to really raise the brace height on that bow to tune it and keep the string from beating my arm guard to death!

Seen those guys bungee jumping? Boing! Bouncing up and down a few times due to all that energy being absorbed and then expended by the elasticity of the bungee cord. After all the energy is spent, the guy just hangs there till he's rescued.

Your bow's limbs do the same thing with B-50. As the arrow leaves the bow, they go a good ways past their normal brace position, then the string pulls them back. The elasticity of the string and limbs go to work to expend the excess energy the arrow left behind.

You've got at least a three phase recoil at the shot. Phase 1) Limbs and arrow start forward, pushing the handle into the hand. Phase 2) Limbs go beyond brace, pulling the handle forward, away from the hand. Phase 3) String pulls limbs back into brace position, pushing handle back into the hand.

And the limbs and string can repeat phases 2 and 3 multiple times before finally expending all the excess energy and coming to rest! (Vibration!)

The low stretch FF, Dyna, 450 strings don't entirely eliminate that kind of recoil, but it's cut w-a-y down.