Well copper, even in a .451 or .454 diameter I'd think might be a bit light and a bit too hard.
You might try tin and silver, or just tin.
Get a .451 mold, preferably with round ball and conical so you can try both shapes. Get some "lead free solder" at the hardware store, and see if the bullet will load, and how well they shoot. The conical, being of more volume will give you more weight in the projectile, but the round ball will let you tell if the alloy is soft enough to load into the Remington.
Bismuth is brittle, and bismuth/tin alloy has bismuth added to add weight..., and if it was to work, I'd look for 40/60 bismuth and tin.
The advantage of the tin or tin/silver would be you're going to be at such a close range hunting with a handgun, that the velocity should be still quite high at impact, while if you were using a rifle and going say 50 or more yards, the lack of mass would cause such an alloy ball to significantly shed velocity.
LD
