For some reason, heavy ball points seem to write "smoother"? Is it just me or is it an inertial thing?

It's for a different reason - ballpoints that are heavy are generally more expensive, and therefore higher quality. Try taking the refill out of the pen and writing with it - you'll find that weight has nothing to do with it.

Then, take one of those Staples ballpoints that come 60 to a box and try writing with it. It's a bad pen, regardless of its weight.

What I meant was the same refill in a heavier pen seems to write smoother for me

Just a thought......... Possibly because the heavier pen weight causes the writer to apply more downward force. The ball seems to work a bit better with more force.

Yeah I agree with RLTodd.

Light ballpoints tend to require you to press harder, because they're so light, whereas heavier ones tend to do some of that for you.
I like ballpoints (if I ever use them) that don't need much pressing to begin with though~

What's a B-A-A-L-P-O-I-N-T?