+1! Could be better? So make it better!
Oh, yes, it all comes together.
I found this 2pdr ballistic test data:
Long story short: after adjusting it appropriately to the scale of a normal 2pdr shell and interpolating the results, we get this table:
| 2pdr AP at 0° vs 260 BHN RHA | ||
|---|---|---|
| T(mm): | BL AP (fps): | BL APCBC (fps): |
| 20 | 1141 | 1163 |
| 25 | 1251 | 1276 |
| 30 | 1362 | 1389 |
| 35 | 1473 | 1502 |
| 40 | 1584 | 1615 |
| 45 | 1695 | 1728 |
| 50 | 1805 | 1841 |
| 55 | 1916 | 1954 |
| 60 | 2027 | 2067 |
| 65 | 2138 | 2180 |
| 70 | 2248 | 2293 |
| 75 | 2359 | 2406 |
| 80 | 2470 | 2519 |
| 85 | 2581 | 2632 |
| 90 | 2692 | 2745 |
If we compare these ballistic limits to the historical data shown in this document here:
When we compare the two sources, we see that the uncapped 2pdr AP has less penetration, and the 2pdr APCBC has more than shown here.
Since the 2pdr AP tested is explicitly indicated to have been tested against an average 260 BHN plate, the 2pdr AP data in the candian table must’ve been normalized to even lower hardness, probably 237/240BHN.
While the 2pdr APCBC data is probably against production armor plate that in this range (up to about 80mm) has hardness generally higher than 260 BHN. Which is why its penetration is lower.
Any way to determine whether large caps are going to function the same way?
I feel like the larger the caliber, the larger the difference in BL for capped and uncapped AP.
What makes you think that? Have you seen any data that suggest this to be the case?
Theoretically, I don’t see any plausible physical mechanism that could make this happen.
No, just a feeling.
Something like the: As the diamter increases the weight of the cap increases exponantially, or something like that.
Well so does the rest of the round, isn’t it?
It all gets increased at roughly the same rate, all by the same percentage, wouldn’t it?
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Probably. But I think that AP shells might get too heavy, when you upscale them.
I think bigger shells are generally shorter than small shells.
Ah, I see your reasoning. Yeah true, after a certain point, higher caliber shells are made shorter to keep weight manageable for the loader. But assuming the cap mass is the same for a given caliber, regardless of how long the rest of the shell is, it will take up progressively more mass, percentage wise, of the total.
But I still don’t think it would have any additional negative effect besides that.
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I think you’re right.
The 76mm M79 is 6.8 kg. The 120mm M358 is 23.1 kg. If the 76mm was scaled to 120mm, it would be about 26.8 kg.
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while we’re on the topic of AP caps. Sounds like an interesting read. https://apps.dtic.mil/sti/tr/pdf/AD0029525.pdf
At this velocity this shell should penetrate up to 40mm of vertical armour. 40mm/9.52mm = 4.2 slope multiplier at 70° angle. This indicates that the glacis plate of the Pz.IV (20mm/72°) would provide equivalent protection in excess of 84mm/0° against small caliber (37mm or 40mm), high quality AP shells.
Can someone check whether the 2pdr penetrates this spot in the game?
Edit: the graph I previously posted was wrong. Here is the correct version.
This is based on factual testing data with steel and tungsten projectiles with various head radii.
As we can see, the german 1.1 CHR 7.5cm Pzgr.39 is expected to have 4% less vertical penetration than an otherwise identical shell with a 1.4 CHR head, characteristic of the british AP.
On the other hand, the core of the .50cal AP bullet, with it’s extremely sharp 5 CHR nose, will penetrate an impressive 16% greater vertical armour thickness.
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Is there any data for sloped penetration with the various head radii?
I have some:
Note that the angles here are in German notation. “30°” is 60° angle as we usually define them.
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That’s interesting. The T33 and T50 have 1.5 CHRs but the ogive is secant instead of tangential.
Same with pointy German 20mm AP that really sucks vs. 30° but is very strong against flat armor.
This projectile has only a 2 CHR nose, not enough to make a significant difference due to it’s shape. It does help it stay intact at 0° against thick armour.
Most of the difference between 0° and 30° pen is due to this shell shattering easily against 30° armour, because of a combination of it’s sharp nose, high hardness of the armour of this gauge (20-30mm) and lack of AP cap as well as restrictive german penetration criteria.
Everything works against it here.
NPL formula generally gives accurate predictions, except for below 1600fps ( < 1 caliber plate) and beyond the point where shell w/o it’s AP cap starts to deform from impact.
Any plans here to also include updating globally-underperforming APCR penetration in this suggestion? And what about the equally-unrealistic-and-oversimplified HE filler penalty on APHE?
From reading this and other threads on the old forum for years, HE filler does not directly reduce penetration. HE filler reduces shell integrity, and lowers the minimum velocity for the round to start shattering on impact. IF that lowered velocity is now in the range the gun is actually firing at, it then appears that HE filler is directly reducing armor penetration.
APCR meanwhile is total nonsense, taking into account the full shell mass (penetrator plus aluminum carrier jacket) for some reason despite that being smeared out of the way on impact and irrelevant to armor penetration. The end result is that nearly all APCR rounds are lacking vertical penetration, sometimes to an atrocious degree. The lacking post-penetration damage is another topic, as are the overestimation of shell shattering and bounce chances for the round type in general.
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