The Navy after Pearl Harbor needed a gunsight for the Wildcat. Previously it was a tube style but the Wildcat got an upgrade to an armored windscreen with no hole for the tube. Until the British MkII was incorporated as the MkVIII, they used the Army Airforce's N3. It only projected a 30mil ring and dot in yellow. The Navy cobbled it into the Wildcat and had it modifyed to a 35mil ring and dot. Only a small number of Army P38 aces could perform snap shots on aircraft tracking across their front. Most gunnery was performed from variations on the rear 6 cone.
I created a 30mil ring and dot in a 512x512 mask today by making the ring 120pixels wide and no mil file. Unzoomed that is painfully tiny. But, it is historicaly accurate. I suspect our default FOV head postion is not human accurate until you hit zoom. At which point the 30mil ring is very usable. I put a 50mil ring and dot in my P38L because eventualy the L3 was changed to use that. Unzoomed 50mil is just usable for aiming. The wire ring sight in the P40's is about 50mil as presented by HTC.
I also created a 50mil K14 star and dot sight which I am using in my american aircraft with K14 gyro sights. In real life you could lock the 50mil star in place. HiTech in effect has done this by not COADing the K14 to be a gyro sight in game. I have moved the center of my cockpit default view to the right like with the P47D-11 to the 50mil star graticle. It works quite well. You can also create a 50mil ring and dot for the left hand projector and move the cokpit center to the left. The was available for bore sighting and if the lead comp star sight failed. You could also drop a filter in place to have only the dot visible on the left hand side. Any player can do this by adjusting their default head position right or left and saving with F10. If they first save the previous head position file it can be used to return the default FOV to center.
Baumer, I'll bet the 100mph MkII ring is 80 mil in diameter....
