How much faster could you throw a regulation 5oz baseball than a 12 oz weighted baseball?
In my opinion, a 12oz baseball is too heavy to throw with especially at full effort. Hence, there would be no need to compare speeds. I personally use anywhere from 3oz to 8oz, I find that 12oz promotes poor mechanics and can cause injury easily. However if you’re determined to throw a 12oz, you should be in top shape and at least 18 years old.
Do not throw weighted baseballs. They are proven bad for a pitcher’s arm.
The owner of that site was invited off this site for constant TOS violations.
I’ll also say that some fairly strong scientific work has been done and shown benefits to weighted ball training. Look for a “program” of conditioning and not some huckster who spews “proven” anything, whether for or against.
I feel that my opinions on weighted balls in the middle. It is OK to train with weighted balls as a warmup or to iron out some mechanical issues in practice but it should not be used as a velocity tool. When pitchers try to add velocity through weighted ball training they throw weighted balls at full intent which is the bad part. Yes, this can amount to a marginal increase in velocity however, full intent with a weighted ball places too much strain on the UCL for the velocity increase to be worth it. There are better, more healthy ways to gain velocity.
There are right ways and wrong ways to use weighted balls. As JD recommended, if you want to use weighted balls then do the research and select a reputable program. Just don’t let weighted balls be your only means to increase velocity.