Many versions of the mainstay heavy MG of the time (Maxim.) Mainly the German MG 08 and the Vickers machine gun, With a calm shooter (Depending on training, which indeed reduced as the attrition went on.) was indeed capable of bringing down enemy infantry at large, in the open at about 700 meters.
But during those mass infantry assaults, the defenders usually held their fire until the usual 250-300 yard mark in order to preserve ammunition and increase efficiency, as sick as it sounds.
Most MG gunners simply set their MG tripod elevation trim for chest/abdomen shots at this aforementioned range mark, and when the order unfortunately came, simply rake fired along the front of the assault...
The 7.92x57mm IS regular ammunition type has the ability to inflict mortal wounds from 0 to 4000 meters, and indeed, some MG 08`s were equipped with sights giving a well trained and confident gunner the ability to land some hits or at least give the allied blokes a reason for discomfort at almost 2000 meters. The MG08/15 used on german fighter planes of ww1, all though having a smaller barrel load (For weight reduction.) and sitting on relatively unstable platforms in comparison, had a slower rate of fire (Increasing accuracy a tad again). In a simulator where theres no real fear of death (And thus increasing the chance and even temptation of taking risks). And with an experienced bloke behind the stick, landing hits at 300-500 meters during the conditions described here, does not sound impossible, allthough knowing he/she wont be able to kill you, the theory is probably to make you do a mistake or simply be awed by his ability, but if you really were that far above and away from him at such an angle, you wont have the time to dive down on him before he counters your move anyways, dogfighting is science

I have played ww1 sims since 6 years of age and dare say I know how to handle any virtual crate with a bit of practice.
I get nervous playing online (Sudden adrenaline rush during a fight.) so my accuracy isnt as good as in single player, but the first kill I ever got online, I started firing and landing consistent raking hits with almost no misses along his entire fuselage at about 200 meters whilst rapidly closing on his SE5a (He was stalling and was sideways so he presented me with a larger target.) I simply kept firing and hitting until it was time to avoid hitting him with my DR.1
And last night, with a bottom left wing missing on my DR.1, I could only turn stable to the right, but still got hits and eventually downed a Spad 13 during many deflection bursts in that turning fight, at a range of about 250+-. So 500 with a perfectly healthy and stable bird really doesnt sound unlikely if the pilot really knows how to handle his crate imho
