...If rifles (with self contained metallic cartridges, no less, putting it on par with early 20th century technology) are a thing, in universe, and as we see here are good enough to use accurately at range and even suppressor technology exists (however primitive it may be)... why the hell would you send a hitsquad into a guarded mansion instead of just having a marksman shoot the kid the next time she's in public/out in the open?
Also, he wasn't producing a metric shitload of smoke every time he fired, so that means some form of smokeless powder.