Quick Overview:
Part 1
The Chieftain (and its variants) can all be overpressured by non penetrating rounds around the turret ring and the gun mantle, despite the Chieftain having more than enough armour in those areas to withstand the explosive blast of shells.
Part 2
The armour of the Chieftain’s turret can be penetrated by rounds that should have no chance of penetrating. This primarily affects apds shots, as the later apds rounds tend to have higher levels of angled penetration.
//(Wrong lol)
Begin part 1:
The first round tested was the saphe round for the M247. This round has only 31mm of penetration at 500m, which rules out the round ever penetrating the front of the Chieftain’s turret. However, in several areas, the 165 grams of explosive filler in the round can overpressure the Chieftain. Additionally, the penetration indicator shows that the round is only calculating 4mm of armour, and thus the round overpressures.
The second round tested was the much more formidable m107 round. This round should obviously have a much better chance for penetration. This is because of the 28mm plate that lines the turret ring. However, the armour dimensions of the rest of the turret are much more sound (around 150mm all over the turret). Despite this, the m107 round will still overpressure areas around the gun.
What makes this even more puzzling is comparing the M247’s saphe round to other high explosive rounds with more explosive filler. For example, the shell mk1 (the high explosive shell for the 17 pounder) has 580 grams of explosive filler, yet cannot overpressure the Chieftain (even on a direct hit to the turret ring).
My hypothesis:
The calculation for the overpressure mechanic is not working as intended, in which, the calculation for the amount of armour that a pressure wave can penetrate through is based on the maximum penetration for the shell. For pure high explosive this works fine as the main penetrating force is the shockwave. However, for rounds such as saphe and aphe, this mechanic is bugged. For rounds with over the minimum amount of explosive filler for overpressure inside of the vehicle will cause overpressure kills, even on nonpenetrating shots.
Begin part 2:
//This part is me being a dumb, please disregard as a problem (although I still think 105mm penning it from 2km is inaccurate, that’s just my opinion)
For this, I will be using the most common apds round for the L7A3, being DM12/L28A1/M392A2 as they are all essentially the same round, however I will refer to these rounds as DM12 from now on. The maximum penetration for DM12 at 60 deg. is 134mm at 0 meters distance. This is quite a lot of penetration, however, in areas of the Chieftain’s turret where the compound angle of attack is 60 deg. the turret has around 270mm of equivalent armour. This same area at a compound angle of 0 deg. is anywhere from 122mm thick, to 153mm thick. Furthermore, as the Chieftain’s turret is a cast turret, it should receive a thickness multiplier of 0.94x, but the cast nature of the turret seems to take away its ability to sustain angles at all.
My Hypothesis:
The cast nature of the turret of the Chieftain is preventing proper calculation of angles. This may affect other cast armour layouts in other vehicles, however, it is clear that it is affecting the Chieftain.