As far as I know 75 mm T45 HVAP wasn’t fired from any other cannon.
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How exactly would it reach such performance? What about the 7,5 cm Pzgr. 40 at 919m/s then? And at 930 and 990?
Do you have any stats on the Pzgr.40 round for the KwK 40?
Edit: I’ve found stats on the overall weight (4.1 kg), core diameter (28 mm) and core length (111 mm), but haven’t found the core weight.
A combination of factors.
First, when already high velocity guns fire a light projectile at an even higher velocity, their efficiency drops, and the muzzle energy decreases. Compare the german 5cm gun firing AP vs firing APCR.
So, logically, we should expect a medium velocity gun, like the M3, to loose less muzzle energy firing this projectile.
Right? Well, in this case the muzzle energy in not only preserved, but actually increased, against common sense.
My theory is, as I know from Hunnicuts books, that this gun had a significant reserve of integrity, compared to many high velocity anti tank guns. So I suspects that this HVAP round was loaded with more propellant than the AP round, and was fired at higher max pressure, at some expense of barrel life.
Secondly, as is usually the case with Ww2 US tungsten projectiles, it had an obscenely heavy core, same 4lb. as the M93 HVAP, almost twice as heavy in fact as that of the German 75mm APCR.
And finally, since for supersonic projectiles the drag force increases with the equare of velocity, beign fired at lower m.v. helps it retain its energy at longer ranger than most HVAP shells.
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4,1 kg 28x111mm 900g core
Ok so right off the bat T45 has a core that’s twice as heavy.
Because the people from the US apparently didn’t really care about conserving their tungsten.
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estimated penetration of the 7.5cm Pzgr.40, fired at 930m/s:
100m: 181/129mm
500m: 156/107mm
1000m: 123/85mm
Funny, very close to the figures for the T45 HVAP.
Estimated performance of the 75mm T45 HVAP:
100m: 186/133mm at 0/30° respectively
500m: 160/109mm
1000m: 126/86mm
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And at 990m/s? (As from L/46 and L/48)
Oh wow, that would be nice.
How do you apply the hardness curve to the penetration calculator?
At the moment, I have found no straightforward way to apply it to the calculation of full caliber shells. It’s better to just use the NPL formula for those cases.
While for subcaliber projectiles at low obliquity, making the K coefficient proportional to the cubic root of the ratio of BHN values of two plates, seems to produce the best results.
Well, the armor penetration depends on the hardness, so you can’t really give one specific armor penetration value. How would you know when you change from one plate hardness to the next?
At best it would be something linear. Like 100mm pen = 260 BHN, 101mm pen = 259 BHN.
But that’s kinda pointless.
In the end you want to know whether a shell is going to pen X armor of Y hardness and Z angle.
Like the T-34s armor is going to give wildly different results than a Shermans.
So at best the penetration formula can take those already known factors into account to calculate a more or less accurate result.
For example, the IS-2 HHA would be much more resistant to the APCR round, afaik.
So the penetration graph that takes that specific range of hardness into account, wouldn’t work for accurate estimations against the 100mm HHA.
The USA supplied pretty much all of the molybdenum in the world during the WW2 years, which meant we could substitute it for both tungsten and nickel in steel alloys no problem. We also had access to sizeable vanadium reserves, which had similar applications. Since our machine tooling and other alloys needed less tungsten, we were free to use it elsewhere. We also had access to all of Latin America’s tungsten reserves to import from, on top of the fact that we were also right behind Portugal in tungsten production. The only strategic resource the USA really struggled to procure in abundance was chromium, at least once we started the production of synthetic rubber.
I made these tables comparing how the tungsten cored 20x139mm ammunition performs in-game vs. what we can tell from historical documentation.
Here is DM43, a well documented round (a.k.a. M601 in US service)
DM63 is somewhat more enigmatic, only information I could find is at 1000m
This reinforces what many of us already know, that low-caliber tungsten core is under-performing in Gaijin’s ballistic calculator.
Sources:
Spoiler
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DM63 uses a gen 2 APDS calculator in game. Which comes with better slope modifiers (divide the flat pen by the respective 60 deg pen, you get aroudn 2.62, which means 2nd generation).
However the penetration values shown match much more what would be expected from a gen 1 APDS design, that is, a sharp uncapped core of tungsten carbide, which makes sense.
So DM63 likely uses the wrong calculator in the first place.
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Good observation!
The difference is definitely lesser as the angle increases.
0° = 39 mm
30° = 24 mm
60° = 5 mm
One thing to note: even if the IRL DM63 is a gen 1, it still beats the in-game penetration at all angles by some margin.
According to the table, pen at 1000m is 70mm. That’s 4mm greater than the 66mm point blank pen we have in-game…
So would one be wrong to assume that the “base” penetration is off by some millimeters, while the penetration drop-off is way too pronounced?
Or is the drop-off correct, but the “base” penetration should be much higher?
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So one quick crash-course in Blender and here I am. This is my first model, so I hope it will serve.
Volume of DM63 core: 5435.56mm^3 = 5.43556cm^3
If we assume the density of Tungsten Carbide is 15,63g/cm^3, then it weighs 84.9578g or ≈ 85g
So now 85 out of 108 grams is accounted for.
The remaining 23g of projectile weight is probably the aluminum nose cone and/or base plate? I will try to model these later.
I’d be grateful if anyone could use this data and/or model for simulations.
Update:
Phew! I finally modeled all the major parts:
Aluminum “Base” Cap - 16.83g
Tungsten Carbide Core - 84.95g
Aluminum Nose Cone - 1.17g
Plastic Sabot - 6.47
It all adds up to 109.4g, only 1.4g over the specified weight of 108g
This difference may be due to modeling errors, different densities, and/or missing tracer cavity (in the core)
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As far as I know, the T44 HVAP uses the same core as the M304 HVAP, so this data is applicable to either of them.
If we consider this relationship accurate, then the BL at angle A will be equal to BL at 0° + 0.667*A^2.
For example: the estimated BL for the german 5cm APCR against 2.5in. (63,5mm) at 0° is 2182fps.
Same plate angled at 46° (Sherman UFP) will be perforated with striking velocity of, at least, 2182 + 0.667*(46)^2 = 3593fps, which is about 100m distance for 5cm L/60 gun.
That’s a weird formula. Shouldn’t there be some sine or cosine be involved to get from angle to a number?
At 30° we already need 27.5% higher muzzle velocity, which doesn’t seem logical.