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.
Doing my part to keep this thread alive.
For the sake of gameplay, IMHO no round should deal so little postpen that you wonder if it is even worth bringing, much less loading into your gun barrel.
Now has APCR postpen improved a little over the years? Yes. But it won’t truly be worthwhile until it deals postpen comparable to solid AP from the same gun.
The same is true with APDS, as well as ammunition types this thread is not about (HEAT, HEATFS, HESH, APFSDS).
Even if the penetration values get corrected for all the APCR rounds like they very much should, those numbers will mean very little if the round does almost no postpen damage. If you can’t depend on it to save you in an emergency, why bring it at all?
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.
It’s a purely empirical formula. It’s meant only to interpolate the data, not to be used to explain or extrapolate.
And you can see how well it does it job from comparing it’s predictions to results from the document I posted.
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I’ve put onto a spreadsheet the data on 30° performance of the US 76mm and 90mm HVAP shells located in that document.
As you can see there is a significant spread of results. After eliminating some of data points related on unrealistic situations (like the 5in. plate of 338 BHN) and others that deviated far too much from the average to be of use, it resulted in this data set.
This is the best that can be done.
Using this model, I applied it to estimate the performance of some well known subcaliber shells, as a sanity check:
Edit: Fixed the 5cm APCR graph.
Because in the data set there was no data on performance of these early tungsten carbide cores for velocities above approx. 3200fps, I’ve shown the extrapolated values with a dotted line.
Edit: As a side note, the german 5cm APCR is scary. If this game used it’s real life performance, the Pz.III’s would be 4.0 material, lol.
Interesting.
Tho where did you get 1135m/s for the Pzgr.40/1?
And by Russian, british and USA testing for the 40 it even got to 1200m/s, how would it then perform?
German firing table.
From here: Pak 38 Pzgr.40 and 40/1 - Axis History Forum
Like I said last time, ( I remember our previous conversation on this topic), the earlier 5cm Pzgr.40 (without a suffix) was lighter and had higher muzzle velocity, nominally 1180m/s, but could be anywhere between 1150-1200m/s, depending on the wear on the gun.
While the later one, Pzgr. 40/1, was heavier and had lower m.v., but better ballistics.
Thats not readable? And i dont see a 5 at the back?
Im not doubting the velocitys and i know of both 1180 and 1200, but i was more interested in the 1135 instead of 1130 from in game.
From the looks of it, the Pzgr. 40/1 would outperform the Pzgr. 39 at any range 🤔
But maybe I’m just imagining things.
In the ammo manual it says it should only be used till 800m.
Even though I feel like that German manuals generally underestimate the performance difference at range.
But I guess the difference isn’t big enough to be worthwhile.
Honestly I don’t remember anymore why exactly I use 1135m/s figure, it was just there in my external ballistic calculator. It might be because I once saw a figure of 3725fps (1135.38m/s) in some allied intelligence report on this gun, but I can’t find it now.
But these are really tiny details that are virtually negligible in the grand scheme of things. More importantly, I believe that this historical german FT is quite simply wrong.
The drag on this shell is simply too high, pretty much same as that on the “H”-type arrowhead design of the earlier shell. In the graph I posted earlier I’ve used external ballistics of M93 HVAP, since it has almost identical external shape to the 5cm Pzgr.40/1.
If we were to trust the german FT, the newer APCR shell would have lower penetration than the older one, up to 500m, and only a tiny advantage (5mm at most) at longer range. I don’t believe that germans would change it’s design just for this.
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