Apart from the cost concerns, has anyone cast with pure tin for smoothbore. If shooting in competition it may have an advantage as velocity is your friend with a smoothbore and paper is the target. I just cast some .600 for .62cal/20 gauge and to be honest I see no problem using them for hunting within the range I would use them (50 ish yards and less). I recover all my projectiles from practice so cost can be reduced.
May also be a projectile for shooters in the Peoples Republic of California as none lead/none toxic, I cast some .440RB to test in my Pedersoli Kentucky .45cal , normally run .445RB with 10 thou patch in that rifle but will try the tin ball with thick patch.