Ok. The LASR's damage rating has yet to be converted to the new system. Medium, as I recall was about four, or five on the old scale. And rounded down to the new system it is 2.5, which is either ADR 3, or 2. Which would go well with the low muzzle velocity. However, the LASR is not on trial here.
The FN SCAR, a IRL Assault Rifle has more then half this weapon's muzzle velocity and some change (2870 fps) plus, it uses ammunition coming close to this already, 7.62x51mm. As it stands, the velocity is too low to necessitate the high damage, even with the DU munitions. Let alone the very high ROF which, I am again sorry to say makes me scratch my head at in regards to the model you based it off of. You're putting out 5,000 FPS, which is 1,546 m/s. If a modern rifle has nearly as much kick as this, then your damage is too high.