Several options for waterfowl loads out there that are legal and double gun safe but they're all expensive.
My choice would be Kent Tungsten Matrix but the price has reached about $3 per shell these days. Bismuth is a little cheaper but the shells have gotten hard ot find since the company has gone out of businss.
Federal Tungsten Polymer is good, but they've stopped making it as of this year so it's going to be hard to find as well.
Hevi-Shot has a new double gun friendly shell as well called "Classic Doubles" but it's $3 a shells as well and I don't know anybody that's tried it yet.