Found bug and seemed to have confirmed.
Luck in the Chamber will proc first every time on (so far) Matador or Party Crasher. I have tested 4 and have one more that has noted the same on 2 of his shotguns.
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The sound is there for me as well. after you reload a shell the next will always have the sound. It doesn't seem to actually have bouns damage though. I tested it vs 32 ogres in POE, the first shot would do the same damage as the next couple of shots. So it seems like the sound is there but not the damage.