Of these, only the German AP-I has an armor piercing power of 8mm (100m), all others have 12mm. 12mm is the same as the armor piercing power of a pure AP round.
Is this really correct?
I have done some research, but have not been able to find any authoritative information due to the language barrier.
I had never heard of the Swedish 6.5mm AP before. Is it a ground vehicle bullet?
It is indeed amazing that it penetrated 25mm steel.
I was curious so I looked into it as far as I could find out.
The above site says “22-25 mm of HB 130 steel plate”.
HB 130 is a hardness equivalent to or slightly harder than mild steel. I am not sure if it can be called bulletproof steel.
On the other hand, the description “8 mm of HB 500 steel armor” is also given.
HB 500 is a very hard carbon steel, about the hardness of hardened and tempered carbon steel. (a little softer than a file).
Both of these results are from 300m, so there is no doubt that it has a high penetration capacity, but the 25mm value cannot be applied as it is in the game.
There’re quite a few standards for RHA hardness, and I don’t know which one War Thunder follows. They typically vary between 300-500 HB. So the HB 500 value is probably close to how it would perform in WT, while HB 130 is definitely too soft.
Most 7 mm class AP rounds have 10 mm of penetration at 300 m in game. If we assume WT uses a slightly lower hardness standard for RHA then it would make them roughly equal. On the other hand, the site also says it penetrates 16-17 mm HB 500 at 100 m, which definitely makes this Swedish AP superior to other 7 mm class rounds at this range. Maybe it suffers from velocity drop off like APCR/HVAP rounds?
The only Swedish vehicle that uses the 6.5 mm is the Strv m/31, which were out of service by the start of World War II, while the site says this AP round was only produced from 1943-44, so it would be ahistorical to give it the round anyway.
My hypothesis is that Gaijin does use standardised formulas for small calibre round penetration, but they have two sets of formulas, one for “big core” and one for “small core” (not standardised terminology, just my concoction), sort of like how there are different formulas for AP and SAP rounds.
So rounds like German 7.92 AP-I (whose low penetration is also corroborated by L.Dv 4000/10) and Soviet API-T have shorter, lighter steel cores and hence use the lower penetration formula. The odd one out is the Italian 12.7 mm API-T that has a shorter core than the AP/AP-I but gets the same penetration (actually, the AP-I round has 1 mm less penetration than the AP round, maybe because its core is very slightly shorter). This bug report for it (Community Bug Reporting System) was denied, but I think it’s more due to it quoting a forum post as evidence instead of a reliable source, rather than a fundamental change in policy. I’ve been trying to find some better documents but frustratingly ADA310314 only gives a diagram for the API-T and not one of the AP/API for comparison.
Meanwhile, rounds with longer, heavy steel cores like the AP versions would have the same penetration as AP. Apparently Soviet 7.62 mm AP-I was like that according to this image of a German document provided by KillaKiwi:
The core of the AP-I round is roughly the same length as the AP round, while the API-T round has a noticeably shorter core.
This also seems to be the case for Italian 7.7 mm AP-I, according to the cutaway diagrams on this site: munizioni - Le 7,7 Breda Safat. The AP-I core seems to be slightly shorter than the AP core, but it’s hard to say how much that would affect the penetration, so it seems the devs just used the same formula. I think the case with the Italian 12.7 mm AP/AP-I could be applied here as the two cases seem similar (just subtract 1 mm penetration from the AP-I round).
Of course this is all pure speculation. If a tech mod could clarify Gaijin’s policy on small calibre penetration (as it was requested here Community Bug Reporting System, a year ago) that would be great.
