The A-5 has been the quintesential "down east" duck/goose gun since John Mose Browning invented it. Have seen and worked on lot's of them. Generally speaking "light" means/meant, as Don pointed out, "low brass", up to 3.25 dram and 1.25 oz. of shot. "High brass" was anything hotter/heavier. Unfortunately today one must do a bit of trial and error as the ammunition folks have such a myraid of powders to play with so that their loads will operate gas guns and make $$$. Best, Dr. BILL