9/- To 13

You find yourself in Poland, near Kalisz, in the year 2000 and your commander has just said, "Good luck, you're on your own," just before a big explosion takes out the TOC...

After a few days of dodging Soviets and marauders you decide you're fed up with the 3-round burst mode of your M4.

You remember your dad talking about how they got authorization, during the Gulf War to "bend" something in the fire control parts that disabled the burst and allowing full-auto fire.

What are you going to bend?

Well, dad doesn't know the whole story.

The fast way to remove the burst mode is to remove the burst interrupter, but that will let the normal interrupter to slide too far left to right in the trough in the trigger, giving a Malf of 16 in full auto fire.

Inserting a spacer the same thickness as the burst interrupter solves this issue.

If you're never going to put the 3-round back in, you can use the burst interrupter as the spacer by simply filing off both hooks.

Knowing this and doing this is Armoury/TL8 (Small Arms).  If you don't have this skill, the default is Engineering/TL8 (Small Arms) -5 or Guns/TL8 (Rifle) -5.

But there's another way!

If there's an M16, M16A1, M4A1, C7, C8, C8A1, or L119A1 laying around that's deadlined for some reason besides the fire control group; you swap all the trigger and hammer parts between them and et voila!

This will give a +3 to your Armoury/TL8 (Small Arms) roll because it's so much simpler. 

Please note that none of this will change a semi-automatic civilian version of an AR to a select fire weapon.

For that you need to do some drilling (and machining with some lower receivers).  That's an Armoury/TL8 (Small Arms) roll at -2 because of the precision required in modifying the lower receiver.  Then you toss the semi-auto hammer-trigger-sear parts and plop in the full-auto or burst parts.

Even if you make a drop-in auto-sear with an Armoury/TL8 (Small Arms) you're still going to need the full-auto or burst parts.

Changing semi-auto parts into full auto parts requires adding material to the parts and some finesse.  Armoury/TL8 (Small Arms) -5 and appropriate tools are required.

Neutering full auto parts to delete select fire is Armoury/TL8 (Small Arms) +5.

Doing all of this legally...  If you already own a legally registered machine gun, you can swap parts to your heart's content.

If you don't have a legally owned machinegun, the police will want to have a chat and you will be booking a room in one of the worst hotels on the planet for an extended stay.

In the world of Twilight: 2000, all bets are off!  There's a slim chance of coming back under control of the chain of command who will object to modifications you've made to your issued weapon.