An ounce of steel has more pellets than an ounce of lead. While it seems like the steel loads are smaller, weight wise, they really aren't, count wise.

Pressure is the devil in the details. Effective steel loads don't produce low pressure readings.

High pressure loads of steel are the cross we will bear in the near future.

More than one old A5 with a thin barrel was bulged before anyone ever thought of steel shot-big sized loads of buckshot do the same thing to thin walled guns of any vintage. Nobody has ever been able to prove a bulged barrel is less effective, but, it sure is ugly.
Best,
Ted