"The GR-1 is capable of accepting 3 different standard projectile lengths (32 mm, 42 mm, and 52 mm) with a unique variable magazine system"
"Muzzle Velocity: 75 m/s."
75 m/s is slower than a lot of bows, and those are fairly big slugs, as compared to a .22 bullet.
What you should expect with this gun is a very curved trajectory and, likely, low accuracy. At the very least, it will need sights similar to what's available for bows, since a few meters of distance in range will have a large impact on where the bullet lands.
The large size of these bullets means they might actually not penetrate much, if at all. (I'd appreciate more spec's than just their length). Yes, they have half the kinetic energy of a .22 round, but that's going to be spread over a much larger impact area.