There is already some unlimited ammo tutorials here on MPGH, but I thought I would make another one. The only difference is mine is a VIDEO tutorial. Enjoy and thank me if I helped.
1. Get a SMG with a silencer.
2. Put it on and press v.
3. Shoot as soon as you press V.
4. Stop shooting after a couple of seconds.
He was the original poster on MPGH as far as I know, I just made a video to explain it more. Give some kudos to him