Yeah, this is not an estimate I will post tomorrow the page from the document were it says it.
The penetrator of 7.5cm Pzgr. 39 is 5.925kg, figure taken from historical German source. So it’s cap+windshield are ~12.9% of total mass.
Edit:
This is not the mass w/o the fuze and filler as might be tempting to assume at first glace, because the M66A1 fuze weights at 1.04lb.
In US methodology it is usual to report the weight of APCBC shells without taking into account the mass of their BC:
So, this one should be interpreted as:
The mass of the M62 APC without cap and WS is 14.7lb - 13.9% = 12.66lb. (5.74kg). This is 82% of it’s total mass (15.44lb)
I would like to thank @MiseryIndex556 for providing the data about the T50E1 shell.
External ballistics of two shells are assumed to be identical.
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According to the Table of Form Factors, the M82 and T50 have similar ballistics.
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Can you continue it to 3200 fps?
The NPL formula is not meant to be used for velocities above 3000fps, but I don’t think there will be much error if we extrapolate it at 0° obliquity.
I have added the german long 88mm for comparison.
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Superior German Krupp Stahl 😜
(I know it’s slower :P)
Because of it’s blunter nose the T50E1 would likely overperform the german counterpart against high obliquity armour. :p
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PzGr 39/43 had an army limit of 3322 against 3-3/8” 241-263 plate at 55 degrees.
T50 had an army limit of 2811 to 3251 against a similar plate. They used different lots of the T50 so I’m guessing they were development rounds.
I mean, I think you should take this result with a grain of salt.
3322fps is almost muzzle velocity for that gun. And do you actually believe that 100mm of cast armour at 60° on an JS-2 is weaker than 86mm/55° RHA?
You should check this 200 post thread on this topic when you have the time: 8,8 cm PzGr 39 Performance - Axis History Forum
That’s fair. Just trying to compare data using the same standard.
Finally, after a long and difficult fight with bad quality scans and clunky user interface of 3D modelling software, I arrived at solution.
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The cap + ws take up almost exactly 22% of total mass of the shell. Hurrah!
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Good to know for sure it’s 22%.
What software do you use?
No shame in using what you have.
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Meh, I use the free version of Fusion 360 :D…
On another note…
I believe I may have figure out part of the issue with the 90mm M82 filler controversy… Which may also be the reason why there are two different values 0.31lbs or 0.44lbs depending on the manual, even during the same time period.
The explosive filler used in US APHE shells, Explosive D (Dunnite, Ammonium Picrate), can only be press loaded. However, it can be press loaded to 5 different densities, ranging from 1.41g/cc to 1.64g/cc.
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Standard loading Density spec for Exp. D in US AP shells is ~1.48g/cc…
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However, I haven’t had the time to make a 3D model of the M82 Shell yet. So I haven’t had the ability to play around with the filler density to see how it would effect the filler mass. But, just from playing around with a cylinder mass calculator, there only seems to be a difference of about 16-17grams when changing from 1.48 to 1.64g/cc with a cylinder of approximately the same volume as the M82 burst cavity.
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I have a full 3D solid model of the M82 I made in Solidworks. I can send you the file.
There is no need to build a 3D model for that. Mass is linearly proportional to density, so a loading of 1.41g/cc will have mass 86% that of 1.64g/cc.
86% of 0.44lb. equals to 0.378lb.
Not enough to explain the 0.31lb value.
Edit:
WIP
I think I posted it before but here are the two versions of 90mm M82:
90mm M82 are the third and fourth from the left
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On the topic of realistic performance of the US shells with rounded rose, like the M82.
Intuitively we know that their performance against thick armour must be a bit lower than that of the shells with a more pointy nose, but how much exactly?
Well, I decided to find out.
First, let’s compare the results we can obtain using the NPL formula with US data on uncapped AP with sharp tip:
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As you can see, the match is almost perfect, so we can safely conclude that the armour quality and penetration criteria used by the US specialists will not influence our results.
Then, lets compare the NPL estimates for a 14.7lb. M62 APC shell tested here. This smaller weight (vs 15.44lb for a combat projectile) indicates that the shell is modified by removing it’s windshield (-0.40lb) and replacing the fuze with a steel plug (-0.35lb.) as well as replacing the explosive filler with the same mass of inert material (+0 lb.)
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If we apply only the adjustment for AP cap (+2% to BL) we are still short of what we see here. In order to see just by how much we interpolate the data and calculate the ratio between the experimental and estimated values:
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As you can see, the average experimental values are ~3.6% higher. This is after we apply the adjustment for AP cap, so the total BL coefficient to use with NPL formula when estimating the penetration of the US APC shells with round tips is x1.02 * x1.036 = x1.056
The results we get from NPL formula with and without this new adjustment:
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So why the decision on the rather round noses?
Intuitively, I would say maybe to get better effect against FHA, even in cases the cap got removed due to spaced armor.
Or in which other scenario would the round nose improve the performance? Against 30° armor?
