I checked and it seems it's flawed indeed, I have 6 hits out of 133, with 57 enemies killed (I don't use it much) While I'm at it, I noticed I have a hit rate over 100% with the Hive Cannon, with 9829 out of 8503 hits, and 388 enemies killed.
Thanks for actually checking yours, I knew there'd be others' that were screwed up! As for the Hive Cannon stat being over 100%, this doesn't apply to the grenades, but I'm pretty sure any time you hit multiple enemies with the same round it gets counted at least twice...
I noticed after I got Explosive Focus and was using it with the Shrieker, which I hadn't used yet in Campaign. After making 40 shots, with about half of them hitting two or more enemies, I checked its Accuracy in the stats and it was just over 150%. It's probably easiest with the Dark Star, but I believe any gun that you've hit multiple enemies with more than you've missed should go over 100%.
Anyway, no wonder... I had forgotten the Hive Cannon (and the Shrieker, although I don't really like that weapon much so I almost never use it) does explosive damage too so that might be the reason. I haven't tried the Dark Star much either, I'll check it next time I play.
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