8,8 cm PzGr 39 Performance

Discussions on the vehicles used by the Axis forces. Hosted by Christian Ankerstjerne
Peasant
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Re: 8,8 cm PzGr 39 Performance

Post by Peasant » 31 Dec 2018 12:28

Something I hope will be relevant: a neat way to describe how several different projectile designs interacts with armour with varying characteristics, is to express the projectile performance in therms of energy required to defeat a unit of LOS of armour. Here we can see how the late German PzGr.39 AP design negotiates slopes: the required energy stays mostly the same up to about 50° and then it drops drastically. I believe it's the effect of the projectile nose breaking off somewhere between 50-60° changing the penetration mode from ductile hole enlargement to shearing of the plug from the armour.

Image
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Peasant
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Re: 8,8 cm PzGr 39 Performance

Post by Peasant » 11 Jan 2019 22:54

Some information that I didnt know which might prove useful:
The changes made for the new PzGr.39/43 introduced with the new 45 deg acceptance conditions in autumn 1944 included the following:

- improved heat treatment of the penetrator, specifically the nose

- changed ballistic cap & windshield design

In addition to this it appears that the shape of the burster cavity was changed as well, wider at the bottom, narrower at the top. Sadly no original German cut away drawings exist for this round, only the polte drawings for the initial prototype 39/43 design which ended up the stop gap PzGr.39/1 with wider driving bands, not to be confused with the small drive band PzGr.39/1 issued in the beginning, which also shortly had the PzGr.41 designation. It's a confusing mix of projectiles used, esp. due to similar designations, safe from the serial number, making it all the more understandable how the people at the USAPG could mix it up.

Three different PzGr.39's compared
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The 8.8cm PzGr. recovered designated PzGr.41:

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Source: https://forum.warthunder.com/index.php? ... nt-7790515

critical mass
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Re: 8,8 cm PzGr 39 Performance

Post by critical mass » 12 Jan 2019 14:58

Never heard about a 88mm Pzgr41 in german sources (includes Referat III HWA development tables).

seppw
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Re: 8,8 cm PzGr 39 Performance

Post by seppw » 12 Jan 2019 18:05

The 7.5cm Pzgr39 had the conical cap eventually, the 12.8cm Pzgr39 had the conical cap eventually, so why didn't this 8.8cm Pzgr39 get it?

critical mass
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Re: 8,8 cm PzGr 39 Performance

Post by critical mass » 23 Jan 2019 18:34

Not necessary for the 88mm pzgr39. Only relevant if target thickness is >200mm for this cal. Under all other conditions, a smaller cap is better (less dead weight wasted needs to be accelerated).
For the 12.8cm/8.8cm Pzgr.39 -TS, which was expected to deal with plates >25cm, the cap was indeed changed towards the thick Army type cap.

Peasant
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Re: 8,8 cm PzGr 39 Performance

Post by Peasant » 04 Mar 2019 15:03

Mobius wrote:
25 Dec 2018 16:13
Whelm. do you have any British Critical Velocity charts on the ballistic capped British 6 pdr? It would be interesting to compare it's ballistics with that of the Russian 57mm and US 57mm M86.

BTW, plotting 88mm MV=780 m/s velocities on the British CV of 88mm small capacity yields these data points.
88mmsmallcapcityOB44.jpg
Mobius, I have good news. we can stop pixel-hunting on these charts. These curves were computed using this formula here:

Image

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With n = 1,43, as the later paper suggests, the R constant is very close to 3260, for 6pdr AP at normal incidence (SD=27)
Here is the calculated graph from excel overlayed on top of the chart:

Image

To get R not so small as to go into decimal values, I've used Kg for shell weight, cm for diameter and m/s for velocity.
Other charts will have slightly different "R"s, mind you.

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Mobius
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Re: 8,8 cm PzGr 39 Performance

Post by Mobius » 04 Mar 2019 15:29

Nice,
I must of missed them but whelm already uploaded firing graphs for other 6 pdrs.

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