I have a rim the size of a junior basketball that is fixed 6 feet high. When I'm bored I pick up a volleyball and just shoot. A friend told me to stop doing it because it will weaken my shot. Is he right? If so, how would I "regain" my shot strength?

If you are just messing around a little, then I don't think there is any harm in it.

Part of what form shooting does, in addition to reinforcing proper form, is it trains release angle, eye level, and knee bend (my opinion, others may argue differently).

So if you are doing it trying to develop good habits, I'd tend to say it forms as many bad habits as good. Your arm angle will drop because the ball won't have to go as high. The shot will flatten out. Your eye train and target angle will also lower. Your knee bend won't have to be as great.

Think about the pronounced form you have to use on a 10 foot rim. That all is lessened on a 6 foot rim.

I'd encourage any 3rd-5th grader to shoot on an 8 foot rim. I sometimes see some players for my school as I drive through my neighborhood playing dunk games on an 8 foot rim.

It's always fine to play around. I think sometimes players and coaches forget that it's a game, and games should be fun.

But if you are doing this with an earnest intent of solidifying your shooting mechanics, I'd hold off, and try to find a basket a little closer to regulation height.

Just my thoughts.