I made a muzzle flash for a gun using SetMaterialCel to change the mat from transparent to the flash cell, then use a timer to change it back. When I shoot, it works, but the same mat on other 3dos have the flash too. Anyone know how to fix it so it only happens to my own gun's 3do and not others? Or is there a better way to do a muzzle flash?

Using MatCel will do it locally everywhere so thats no good, Do it the savageX way, he used a node teleported. I suggest you look up one of his tutuoirls or his TC

take my advice (and ss3 proof that it works), get to grips with Pjed and use keyframes to do the muzzleflash.
its so much better!!!

if(getThingFlags(source) & 0x8){
  do her}
elseif(getThingFlags(source) & 0x4){
  do other babe}
else{
  do a dude}