12.08.2010, 23:21
I have repeated your procedure for a few aircraft, and my conclusion is that NoWonderdog must have used a wrong assumption for his work in relation to the ring size of gunsights. His rings appear to be twice the size they should be.
It seemed to be a practice of the USAAF to refer to the ring radius in their manuals (eg. Aircrewman's Gunnery Manual), yet as your first quoted comment indicates, the pilot's practice was to use the diameter as a measure of field coverage. The latter is only natural as one would not use half target to match the ring radius. There are numerous references to ring diameter, rather than radius, in various descriptions of gunsights and their use.
The USAAF must have changed their approach at some stage, as the navy/ground attack reticle from SDB-5, marked "100 mils" must refer to the diameter. It has two rings 100 and 50 mils and an additional vertical scale in steps of 10 mils (20 mil steps would have been quite useless for a gunner).
From what I managed to find out, the MkVIII gunsight used 70 mil diameter ring (with gaps), while K-14 gunsight used 70 mil fixed ring, with the gyro marks worked on the basis of 50 mil diameter convergence.
It seemed to be a practice of the USAAF to refer to the ring radius in their manuals (eg. Aircrewman's Gunnery Manual), yet as your first quoted comment indicates, the pilot's practice was to use the diameter as a measure of field coverage. The latter is only natural as one would not use half target to match the ring radius. There are numerous references to ring diameter, rather than radius, in various descriptions of gunsights and their use.
The USAAF must have changed their approach at some stage, as the navy/ground attack reticle from SDB-5, marked "100 mils" must refer to the diameter. It has two rings 100 and 50 mils and an additional vertical scale in steps of 10 mils (20 mil steps would have been quite useless for a gunner).
From what I managed to find out, the MkVIII gunsight used 70 mil diameter ring (with gaps), while K-14 gunsight used 70 mil fixed ring, with the gyro marks worked on the basis of 50 mil diameter convergence.