I found that, thanks to Historical: Reunification War, one could calculate the full kinetic energy and, therefore, impact velocities of every kinetic-kill weapon in BattleTech. In kilotons of TNT-equivalent and meters-per-second, respectively, here is the full list:
> Mass Drivers
>> Heavy:
>>> 70 Kilotons
>>> 80,675 m/s
>> Medium:
>>> 50 kilotons
>>> 83,506.5 m/s
>>Light:
>>> 30 Kilotons
>>> 91,476.75 m/s
> Gauss Rifles
>> Naval
>>> Heavy:
>>>> 15 Kilotons
>>>> 501,038.9 m/s
>>> Medium:
>>>> 12.5 Kilotons
>>>> 511,370.7 m/s
>>> Light:
>>>> 7.5 Kilotons
>>>> 560,178.5 m/s
>> Ground
>>> Standard:
>>>> 0.75 Kiloton
>>>> 224,071.4 m/s
>>> Heavy:
>>>> (Short/Medium/Long Range) 1.25/1/0.5 Kilotons
>>>> (Short/Medium/Long Range) 204,548.3/182,953.5/129,367.7 m/s
>>> Light:
>>>> 0.4 Kiloton
>>>> 231,420 m/s
>>> Improved Heavy:
>>>> 1.1 Kilotons
>>>> 191,883.3 m/s
>>> Magshot:
>>>> 0.1 Kiloton
>>>> 204,548.3
>>> Anti-Personnel:
>>>> 0.15 Kiloton
>>>> 224,071.4 m/s
>>> Hyper-Assault Gauss Rifle 20/30/40
>>>> 1/1.5/2 Kilotons
>>>> 224,071.4/224,071.4/224,071.4 m/s
