How you gonna make one?
A bullet made from chopped fiber in a matrix is possible. They could be cast or machined from extruded stock.
Contemplating fabricaton of a bullet made from sheet goods gives me a headache. About the best you could do is cram some pre-pregged material into a die, mash hell out of it to get it consolidated, then cure with heat to get the bullet out of the die in a sensible amount of time.
If you want to experiment with the viability of this idea, buy some nylon 6/6 rod and turn bullets from this stock. This is a glass filled nylon that is close enough to a carbon product. You might be able to find some carbon filled nylon, too, but I'm not going to look for it.
Use 0.06 to 0.065 pounds per cubic inch to estimate the weight of your bullets. Lead alloys are essentially 0.395 pound per cubic inch.
Folks have incorrect notions that carbon/epoxy "things" have magical properties. I'm not going to go into the reasons why it falls down in certain applications and where it is best used, but remember this in the context of using it for a bullet; it's burnt string and glue.
A low speed primer powered bullet is possible. There are better choices, ones that are not filled with carbon or glass. I don't want to run those materials down the barrel of any of my guns.
Try to run one at high speed and you'll probably not get it out of the bore when the plastic matrix melts.