I've got a 12 gauge Browning A5 light that I love using for pheasants and chukars. It's the old Belgian version so it won't shoot steel without some modifying. I want to take my daughter duck hunting and let her use the A5 - she's shot skeet with it before and has done just fine. Is bismuth soft enough to shoot out of that barrel?

Bismuth is fine. I use a product made by Kent called Tungsten Matrix. Another product is Nice Shot. None of these products are cheap but they will not damage your gun barrel like steel can. What choke do you have on the old Browning?

100% agreed!!! My dad shoots it in his Belgium A5 and Fox double for duck hunting with us on Thanksgiving day duck hunt and it does just great!!!! Ducks don't know any difference!!!!

Yes, bismuth is safe in your older Browning, as is ITM (tungsten matrix) and NICE shot. Another one not mentioned is ITX shot from Ballistic products; however, to the best of my knowledge, it is currently only available as a reloading component.
Two other loadings that are available in loaded shotshells are "Tundra", by Fiocchi and Hevishot classic doubles, both of which are safe in older, fixed choked guns.
As stated previously, none of these alternatives are as cheap as steel shot.
Good luck and good hunting...............

I'm now down to my last box of bismuth. We got fourteen ducks and a goose, and had a day she'll never forget. Appreciate all your help!

Sounds like you had a good time and made some great memories.....congrats!