This comes from me, before the "max 7 free actions" ruling in 1e. Throwable shields are a free action to throw, which is arguably an attack roll. Belt of returning makes thrown object return as a free action. Quick Draw, iir the right feat, lets you draw your weapon as a free action. This means you can, as a series of unlimited free actions, do unlimited attacks per round.

Throw in Hammer the Gap, Clustered Shots and one other feat I can't remember and you have unlimited damage in one "attack." Doesn't matter what the DM determines as the base damage of the thrown shield.