looks homemade. maybe it's designed for most common pistol caliber aka 9mm, this caliber either would work or don't. one can't tell exactly because bullet energy isn't enough to blow out half of your brain, rather it's perforate insides of skull and leaving hole on the other side, if you miss a brain artery you'll likely to end up imbecile and if you get medical attention and cerebral bleeding has managed ones fate is the same
i would ask for sawn-off 12cal tho, because it would for certain evaporate half of your brain if aiming straight at the skull but maybe you know already that if you gonna aim at chin you can miserably fail and it's will be even worse as your face is disfigured for life also probability of miss with grave consequences increases w/out practice i'd make shooting somewhere where it's safe for certain to know what to expect from gun's recoil
third aspect to consider is gun dealing and dealer. gun dealing is dangerous and shady, the best possible outcome from the worst outcomes of such deals is being scammed. others are getting in trouble with mafia/cartels next one is being jailed. i hope you know exactly what you doing when having contacts with black market