I've started getting into a "4 fingers per string" method of shredding, and i've found my weakest finger to be my ring finger. It can't stretcg as far as theothers and isnt very accurate. Anyone know any excercises to build ring finger dexterity?
Make your own exercises, they will work better on you than anyone.

Come up with something, anything really. That is hard for your ringfinger, then slow down and practice it perfectly and then speed up a little. Do it for a few days and it will work wonders.

It´s like im learning alternate picking atm, and my problem is shifting posistions when doing long runs. So i practice that, come up with stuff with lots of shifting and it works great!

Good luck!
One thing I still do on occasion is rest all 4 fingers on the B string. (Just touching the string - not pressing down)

Then one finger at a time, I'll hammer slowly on the G string (fretted to open) without lifting or pressing the other 3 fingers. They have to stay completely relaxed while you trill the single finger.
If you're anything like me... you'll find this most challenging and beneficial for the ring finger.

Here is another great exercise for the ring finger. Do this between fingers 2-3 and 3-4.
Stay relaxed and accurate, it's not for speed... it's for building up control and dexterity of the ring finger.

(Repeat each 8-note pattern one minute before moving to the next).

That's just 2 things you can do... but make up your own as well.
If there's something you have trouble with... make an exercise out of it.
good luck