There's three basic levels of using this glitch from what I've found so far. The first is using feeder guns from your loadout only. Five and six feeder loadouts work well, although it's possible to have up to seven. The second level you can use in solo or co-op, and involves a player first setting up full floor guns of one type (P90 and FMG9 are great choices). Then with this particular gun type as one of your feeders and another of same type but with a scope or other upgrade. Once your P90 / P90 + red dot guns are empty, walk over a full P90 gun on floor and these guns in your hand will refill and allow you to keep reloading them. Do this for all of the P90 guns on floor. In the third level, your teammate in co-op sets up the P90s for you, from a slot that isn't feeder. He does this on multiple waves, so that you can reload from thirty P90 guns each time. When you finally load your grenade launcher, you can have many tens of thousands of tubes. You may then do all the shooting, but during breaks be setting up say full FMG9 guns on floor so that your teammate will eventually have many tens of thousands of tubes or RPGs. The second and third level require a high degree of discipline, making no mistakes. I achieved over twenty five thousand tubes on this third level, but made numerous mistakes in attempts prior to succeeding. The number of tubes you add maximum for a wave break, is 300 multiplied by max floor guns which I think is 30, so 9000 added each time. All LMGs and the P90 provide 300 rounds per gun, all other guns are less, with next best being FMG9, MP7, MP9.