[TheDS1337]

Try hooking EffectDispatch temp ent using AddTempEntHook and block it if m_iEffectName == 3 (CS_MuzzleFlash index)

PS: here's a dump of EffectDispatch table:

Dumping table EffectDispatch indexed 12 out of 19, has 15 strings [1024 MAX]

	error indexed 0 out of 15
	gunshotsplash indexed 1 out of 15
	KnifeSlash indexed 2 out of 15
	CS_MuzzleFlash indexed 3 out of 15
	csblood indexed 4 out of 15
	ParticleEffect indexed 5 out of 15
	ParticleEffectStop indexed 6 out of 15
	GlassImpact indexed 7 out of 15
	Impact indexed 8 out of 15
	RagdollImpact indexed 9 out of 15
	TracerSound indexed 10 out of 15
	Tracer indexed 11 out of 15
	watersplash indexed 12 out of 15
	waterripple indexed 13 out of 15
	bloodimpact indexed 14 out of 15

PS 2: I am not sure if it removes the first person muzzle, perhaps the third person one, if it didn't work you'll have too check the info_particle_system parented to that weapon and remove it