The tank pressures up to 3600 vs the aluminum tanks 3000 so there's more energy there.
Then the valve has changed to ensure more gas flow. Doug Noble did development on this for several years (prior even to African Air Arms conversion kit) and it seems Airforce took his research (are they crediting him?) and copied it for themselves.
I have a Doug Noble Texan .457 and it gets as good as their reported numbers, and actually a bit better.
