[Crazycarl]

	"railgun.halfcharge"
	{
		"channel"		"CHAN_WEAPON"
		"volume"		"VOL_NORM"
		"pitch"			"PITCH_NORM"
	"CompatibilityAttenuation"	"1.0"
		"wave"			"ambient/energy/zap8.wav"
	}
	"railgun.fullcharge"
	{
		"channel"		"CHAN_WEAPON"
		"volume"		"VOL_NORM"
		"pitch"			"PITCH_NORM"
	"CompatibilityAttenuation"	"1.0"
		"wave"			"ambient/energy/zap9.wav"
	}
	"railgun.overcharge"
	{
		"channel"		"CHAN_WEAPON"
		"volume"		"VOL_NORM"
		"pitch"			"PITCH_NORM"
	"CompatibilityAttenuation"	"1.0"
		"wave"			"ambient/energy/zap5.wav"
	}

Those are HL2 sounds, so you won't find them in the FF folder. You can either create those .wav files, or edit fortressforever\scripts\game_sounds_ff_weapons.txt to point to another .wav