- I shoot unleaded exclusively for several years now. On average, the accuracy seems as good as lead for ~2/3 of the distance of that lead pellet. So a rifle that shoots a 1" (2.5cm) group at 45 meters with a good lead pellet, might now only be able to shoot 1" at 30 meters with a good unleaded. I've only had luck with the diabolo shapes, the plastic saboted steel tipped pellets haven't been accurate in my guns.
That said, I can "good" groups at 50m with H&N Baracuda Greens and Predator GTOs, but only in .25. The .22s start to scatter by that distance. My guess is that with practice and optimization, I'll get there with the .22s too. But yes, lead pellets will inherently be more accurate because with the extra density, their BCs are better. If that accuracy is my expectation then I will be disappointed. But compared with throwing rocks, my second backyard option, I'm very happy with unleaded pellets. And there are some that just happen to shoot really well in some guns, so if one has a gun that prefers lightweight pellets, unleaded might be worth a try.
- I still have to try slugs or heavier-than-commercial unleaded pellets (thanks, NOE!), or cast bismuth projectiles, which weigh about as much as lead.
- Tin is only slightly harder than lead, both Mohs 1.5, and Bismuth is only a little harder at 2.25. Relatively, even soft steel is much harder, Mohs 4.5. I wouldn't worry about wearing out the barrel with any of those metals. Maybe wet patch clean once in a while, as lead, tin or bismuth oxides can be as hard as steel.