I’ve killed 400 people with a pistol several times and only got 2, it doesn’t make sense. It’s also happened to me with the “kill so many enemies with special weapons” option. I kill 40 with the grenade launcher and it gives me 5.
The best part was when I got 15k points for the jumbo tank, I was 10k short and he didn’t give me the tank until the next day ._.