It doesn't need to be as heavy as a real .50, because it's sharper and sturdier. It can probably just stab directly through an unarmored body's soft tissues without stopping. But any sort of armor will stop it, because it's not heavy enough to just punch through. I think that makes sense.
...You don't know much about bullet ballistics, do you? First, making the bullet heavier increases the energy it has at a given velocity, and you can put more energy into a heavier bullet because it doesn't leave the barrel as quickly. Next, sharpness, at least at the level of difference between a
.308 and a crystal, matters very little. Flesh parts pretty easily at these speeds, and it still needs to force it to the sides. Lastly, why do you think crystals are sturdier? During volley fire they shatter into lots of pieces and they shatter after they've hit the target. Bullets pretty much maintain their shape unless they hit a very hard target.
Beyond all that, you don't want anti-personnel bullets to be good at penetration. They'll go through the people and waste most of their energy. That's why we have hollow points, and why crystals are wonderful for armor- they explode after they penetrate, meaning they act like a magical AP hollowpoint.
And Piecewise specifically said it was good at penetrating armor. Your first post about this had his quote in it saying so.
Your rifle has less muzzle velocity and less muzzle energy than a .50 caliber machinegun, so it's unlikely to break the shooter's hands... much. Getting some of the recoil compensators from a gauss rifle would be a good idea in any case.
I really probably won't. This gun, considering how effective it seems, is probably going to be expensive
and have a decent str requirement. Reducing the latter will only exacerbate the former.