Hrafnagud
Posts: 87
Joined: 12/9/2018 Status: offline

It's not quite that simple. Accuracy is different for various weapon types (and not relevant to a large number of them). But let's assume you are talking naval guns. I have developed my own formula to "fit" values to the values assigned to devices in DBB. For naval guns, the accuracy is derived not just from the practical rate of fire, but also includes sectional density of the round, muzzle velocity, and the quality of the mount (i.e. faster traverse and elevation rates mean higher accuracy). These are all then smoothed by a range factor (I use 15% of maximum range). The formula I use is ROUND((<Sectional Density>^0.25)*(<Practical RoF>^0.5)*(<Muzzle Velocity>/762)*(<Mount Factor>^0.25))/(<Range Factor>^0.1/1.9),0) Sectional Density is (Projectile Weight in Kg)/(Pi*(Calibre in mm/2000)^2). So the 46cm APC Type 91 with a projectile weight of 1,460 kg and calibre of 460mm has a SD of 8,785. Practical RoF is just that  not what the maximum rate of fire is  the sustained rate of fire. For the Japanese 46cm/45 T94, that is 1.75 rounds per minute. Muzzle velocity is in meters per second  for the 46cm/45 T94 firing the 1,460 kg APC projectile, that is 780 meters per second. Mount factor is based on the elevation and traverse range of the mount, as well as the rate at which elevate and traverse can take place. I calculate this factor by taking the elevation range times the rate of elevation in degrees divided by 90, plus the traverse range times the rate of traverse divided by 90. For the 46cm T94, the elevation range is 50 degrees, rate of elevation change is 8 degrees per second, the traverse range is 300 degrees, rate of traverse change is 2 degrees per second. So my mount factor is (50*(8/90))+(300*(2/90)), which for the 46cm T94 calculates to 11.11. (To put that into context  a 5"/38 Mk 24 on a single EBR mount on a Fletcher DD has a mount factor of 121, due to much faster rates of elevation and traverse). Range factor is simply 15% of the maximum range in feet, to the power of 0.1, divided by 1.9. For the 46cm T94 firing APC, max range is 42,030 yards, 15% of that is 6,305. To the power of 0.1 becomes 2.4, and divided again by 1.9 gives a range factor of 1.26 (the greater the range on the weapon, the higher this factor will be. A naval gun with a maximum range of only 4,000 yards will have a range factor of 1). We now adjust these values as follows: Sectional density to the power of 0.25  8,785^0.25 = 9.68 Rate of fire to the power of 0.5  1.75^0.5 = 1.32 Muzzle velocity divided by 762 = 780/762 = 1.023 Mount factor to the power of 0.25 = 11.1^0.25 = 1.83 These values are all multiplied together to get a revised value of 23.92. That value is now adjusted by the range factor, that is, divided by it. So 23.92 divided by the 1.26 we calculated above, to give a calculated accuracy of 18.98, rounded to 19. The same calculation gives the 16"/45 Mk 7 firing Mk 868 APC an accuracy value of 23. Compared to the Japanese Type 91 APC, the US projectile has a higher sectional density, slightly lower muzzle velocity, practical rate of fire of 2 rounds a minute versus 1.75, but the major difference is the mount quality (19 versus 11). Hope this helps  I have derived other calculations to try and fit other weapon device types. With dual purpose weapons it gets even more complicated, as accuracy is adjusted with effect to provide values that "fit" for the AA accuracy field.
< Message edited by Hrafnagud  10/18/2021 8:57:42 AM >
