I bought an AR-7 (.22 "survival rifle") when I was in the Navy, took it to a range, aimed, slowly squeezed the trigger like my dad taught me, brrrrrrt! Mag dump. Me: WTF?!?!?!
New mag, point downrange, pull trigger fast/hard, bang! Release trigger, bang! Me: WTF?!?!?!
Take "machinegun" back and get one that works like it's supposed to. Still a crap rifle and didn't keep it long.
See how the trigger has to catch the hammer to prevent it from going all slam-fire? If the difference between the front and rear catch is off a few thousandths, you get a binary trigger, and if held right in the "sweet spot", a slam-fire F/A!