I just got off work. I'm bored. I have a tape measure.
My forearm (wrist to elbow) is about 12". At the largest point, it's 13.75" around. About 3.5" down from the elbow, the muscle starts to taper in dramatically. It looks pretty cool to me.
The thing is... small joints are a good thing in bodybuilding. If I had a 34" waist instead of 29", I wouldn't even look big. With my small waist though, I look a lot bigger than I really am.
If you still think they need work though, go above 10lbs. Whenever I do reverse curls, I do sets of 10 at 40lbs-60lbs. Ten pound weights aren't really going to put the mass on. I think a decent amount of the mass in my forearms is from just doing heavy back work without straps.
Edit:
Check out this photo of Lee Priest. His forearm muscles taper in around the halfway point, too.
