FYI:

Now this may come as a surprise, but the boom is more likely to buckle
if a rigid vang is used to lift a weight at the boom end than if the
same load is upward (as applied by a sail).

In the upward case the boom wall is being pulled out by the vang -an
effect opposed by tension in the boom surface due to the bending moment.
In the weight lifting case, the lower surface is in compression and is
being pushed in by the vang so that wall buckling is far more likely.

Cheers