Not much worried about bore damage, but I share all the other concerns. Shooters have been using lead for centuries for a reason - because it works, and is much cheaper than gold or similarly dense metals.
If non-lead projectiles are to become a success, they will need to be designed differently from lead pellets. Pellets that copy lead Diablo designs in tin, zinc, whatever, are unlikely to succeed. They may do well at 10 or even 25 metres, but not usually beyond.