Check the jaws by inserting something hard and ground----an end mill
shank,
for example, or a drill blanks if you have them. You want this item deep
in the chuck, so the jaws grip at the very back, or inside the chuck body.
Snug up the jaws (lightly, don't get down on the wrench), then see if you
can insert a feeler gauge between the jaws and the chucked item at the
outside end. If you can, the chuck is sprung. It can be salvaged by
grinding the jaws, which we can talk about if you find that's the problem.


FWIW, after getting your chuck clean make up a fixtrue like so:
http://lathe.com/tips/chuck-jaw.htm (Scott Logan's web site)
Then use a carbide boring bar to just shave a RCH off each of the jaw ends.
Everything ends up square and right on center at that diameter.

Karl