Daniel,
You have asked your question in a way that requires a lenthy answer. If what you meant to ask: will my gun be harmed buy shooting steel, the answer at least requires you tell us what gun you are shooting. If a double, the best type to stand up to hard steel shot would be one that has chrome lined barrels with chokes restricted to no more than modified, but better light modified or improved cylinder(steel patterns tighter than lead anyway). Because steel shot maybe harder than standard bores it could mar them, especially through the choke restriction. Steel also creates a hammering effect as it passes through the chokes and double guns may suffer from it (barrels and ribs come loose. Choke tubes, if your gun takes them, could help you. Also waterfowl loads usually offer some stout recoil and a gun built to take recoil in the wrist would be better too. At the ranges you say you are shooting- steel should be effective in #2.
