I've often wondered about bullets other than lead, one that comes to mind is zinc alloy of which there are a bunch of different kinds commonly called pot metal. I know it can be easily cast having cast a steam engine out of old carburetors' although the melting point is a lot higher, it cast really nice. I've never had a bullet mold to try it in though. The weight would be less than lead for the same size bullet might be an advantage I don't know.  Hyper velocity projectiles maybe. Anybody else have any thoughts on this?
		
		
	 
Scalar -
Howdy !
I’ve read of guys casting bullets with Bismuth,  which is a fairly heavy materiel for not being lead.  Bismuth is a non-toxic heavy metal, that has a low melting point.  It has been used for some shotgun pellet ammunition.  This would mostly be for a lower velocity application.
For some higher vel applications, it might be possible to wrap a lead, zinc; or Bismuth bullet with a paper “ patch “, or similarly…. wrap w/ self-stick ( nylon example ) tape.
Within certain calibers, it is possible to ( in some instances ) shoot a sub-calibre bullet in a larger calibre rifle; via use of a “ sabot “.  Remington used to offer 55gr .224” cal bullets
held in .30 cal sabots, and marketed as .30-06  “ Accelerator “ ammo;  for one example.
Sabots are used frequently in muzzle loader applications, one example would be shooting a .45 cal bullet from a .50 cal muzzleloader.
In recent years, one has been able to buy bullets “ turned “ from brass or solid copper.
The are even some ELR shooters,  that “ role their  own  “ brass projectiles.
For something more exotic, water ice can be made very hard, when cooled to cryogenic temperatures.  With use of an appropriately dimensioned  and sealed “ mould “, a bullet could be cast using water…. and then cryo-cooled to final hardness.  Such a bullet probably would benefit from use of a “ gas check “ fitted to its base.  It also might work 
( better ) if “patched” as mentioned above.
One hyper velocity non-lead projectile is a “ flechette “.  These are sometime impact-formed steel projectiles, that weigh a comparable amount to smaller calibre light varmint bullets.  These were known to have been used in the Viet Nam war, sometimes as  
“ cargo munitions “ carried in large quantities; for ariel delivery from a outer case that splits open to deploy its cargo.  There are flechette shotguns rounds available for purchase.  During the Gulf War, one of our 2 battleships fired a few special purpose
16” shells; loaded w/ a large qty of flechettes.  This was done as a diversion, to draw attention away from the US armored swing around Western Iraq.  One coastal Iraqi complained on world news, that a flechette had penetrated the concrete wall of a nearby building; and then still penetrated completely through the fleshy upper portion of one of his thighs.… showing the wound to the camera.  For anything remotely approaching accuracy, a flechette fired for a rifle ( smooth bore or otherwise ), would need some sort of sabot; or discarding light wt spacers.
With regards,
                        357Mag