Both the US and England were clueless to the ineffective combat distance of rifle caliber MG until after they got drubbed over it by Germany and Japan. Yet both taught the 100mph principle for .30cal rounds at 200yds from their WW1 experiences.
By 1943 effective combat distance was 300yds, harmonized for 250yds for the RAF. The AAF determined max effective combat range in the air at 1200ft because of the AN\M2 50cal. Harmonized for 900ft, while teaching the 100mph reticle ring principle at 300yds. AAF, USN and RAF all taught the 100mph principle at 300yds by 1943.
1939-41 combat speeds were slower, and at least for Britain, firing primarily rifle caliber rounds. RAF command at the time used "theory" to dictate harmonization of 400-600 with bombers being the primary target. Wide patterns were theorized to cover the bombers with a hail of rounds. (USN came up with the same idiot concept because they were only concerned about Japanese bombers.) RAF pilots discovered quickly during 1940, rifle caliber rounds were useless past 200, and you needed to concentrate them to cause any real damage. That is where 150yds came from. The hispano increased the effective combat range for firing solutions, which increased to harmonization to 250 with maximum combat range at 300 as they became standard inventory.
Germany's MG FF 20mm in 1940 had horrible ballistics, limiting it to a 200m effective combat range. The E model 109 with wing mounted MG FF were converged at 200m. By the time of the MG151/20 as standard equipment on 109 and 190, 225-250m was effective combat range for fighter to fighter combat. You can extrapolate for the Japanese based on the ballistics.
250m = 273yd
I have a photo of a spitfire sighting tree where the left hispano is aimed slightly higher than the right for a IXb at Biggen Hill. Harmonization at that time was for 250yds. Sounds familiar doesn't it? That is the default convergence for the hispano in all of our spits.
