Remove "Clown-Cartridge" as a Weapon-Perk/Ability from Rocket Launchers. Replace it with following community-imagined perk:
"Make it take it" - "2 Kills With 2 Rockets From This Launcher Will Give You 1 Additional Round Of Ammunition."
This challenges players to use their skill with their weapons, and rewards their skill with an extra round of ammunition, accordingly, rather than granting them additional ammunition from glitch. For Rocket-Launchers that have the ability to hold 3 rounds in a Cartridge, this offers a chance for as many as 4-rounds.
However, I also suggest the following: "Make it take it" would be in the same slot as "Tracking" perks, so it cannot be used in combination with "Tracking" launchers. It would essentially make it OP.
MAKE SURE that getting 2 kills with 1 rocket does not grant you the extra round, so there is no way to exploit this as a "glitch" to get 5+ shots.
Clown Cartridge is just kind of a "dumb-luck" perk, as it is. I think people get enough rewards for "Dumb-Luck" in Crucible Matches, where as being rewarded for ACTUAL SKILL is a rare thing, indeed. (I'm looking at you, RNGesus).
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Simpler fix would be to temporarily remove the cocoon perk.