I regularly practice at 500 yards on human profile targets with my M-14 & I can keep a nice grouping in the head or chest save the stray "flyer" here or there. But Purpose built sniper rifles are not exactly what is being discussed here, it's like comparing apples to oranges. Both fruit, both sweet, both grow on trees but there are few other similarities.
1000 yard .50 cal wing mount A/C to A/C shots are not impossible, not very common irl WWII combat I'm sure we can all agree, but possible. Nose mounts would be even easier but probably not much more common because of the nature of the combat. If you die here, it's no big deal, if you died in real life combat it turns out, that was a very big deal. It's not as likely that anyone would have chased a target for as long or as far as we do in AHII in enemy territory etc. without frantic radio calls for "Get this freakin' guy off my oscar people!" being answered in force; where here in AHII we ignore the pleas of our comrades because it's all in fun & they can just pick out a new ride & up again.

Edit: Nice post Bat, I like the explanation with pictures, it holds my attention better than text alone lol