OK I will start with the mac 10. Also 2 things. Can you make a working trigger with this method, if so how?
I'm going to take it that this isn't a troll, and that you are just young. A working trigger? It's a cardboard prop, what were you expecting it to fire?
If you simply mean a moving trigger, you would have had to design it into the core. You'd need a slot and retaining hole for a spring, then a pin through the trigger and the core as a pivot point.
If you mean as a switch for some LEDs or similar, then you could use a push to make switch, or a micro-switch buried in the grip. Again this would have to be designed in before you build the core.
And if I was to want to make a muzzle (i think there a bit better then silencer's) How exactly would I do that?
Go back and read the section on materials and it will tell you that I use plastic pipe for barrels, scopes and whatnot.