g_weapon.c

This is where you will find how to alter the damage for the gauntlet, machinegun, railgun and the shotgun, because they set the damagere in here, and the other weapons fire various types of missiles so we'll get to them next.

Under each weapon just look for DAMAGE = xxx where the xxx will be a number which determines the amount of damage done, the lower the xxx the less damage will be done, I've listed them below respectively if you want to search for each:

Gauntlet = damage = 50 * s_quadFactor
Machinegun = MACHINEGUN_DAMAGE
Railgun = damage = 100 * s_quadFactor
Shotgun = DEFAULT_SHOTGUN_DAMAGE

bolt->damage = 100;
bolt->splashDamage = 100;