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 » 17 Oct 2020 13:14

Thoddy wrote:
15 Oct 2020 06:51
You wrote
"Mobius, I have good news. we can stop pixel-hunting on these charts. These curves were computed using this formula here:"
...
I concluded you had derived the formula for use in Excel as well as the de Marre and Thompson formulas.
I tried it also but failed.


May you can copy the pieces to the forum? or in a PN.

Thorsten
Alright I think I understand what you mean.

Take for example this chart here for 6pdr shot: https://i.imgur.com/Oyy1r7s.jpg

You can calculate with extremely high accuracy the relationship between thickness and critical velocity for perforation with this formula:
Image

or the same in explicit form relative to V:

Image

Using K = 1807 and n = 1,43

I went into more details DeMarre and similar formulas here: viewtopic.php?p=2282814#p2282814

Thoddy
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Re: 8,8 cm PzGr 39 Performance

Post by Thoddy » 17 Oct 2020 23:51

Thank you

Valid for undeformed projectile?
"Meine Herren, es kann ein siebenjähriger, es kann ein dreißigjähriger Krieg werden – und wehe dem, der zuerst die Lunte in das Pulverfaß schleudert!"

Peasant
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Re: 8,8 cm PzGr 39 Performance

Post by Peasant » 18 Oct 2020 14:08

Thoddy wrote:
17 Oct 2020 23:51
Thank you

Valid for undeformed projectile?
Yes.

Peasant
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Re: 8,8 cm PzGr 39 Performance

Post by Peasant » 29 Apr 2021 11:53

Image
The way data is presented in this report is inconsistent with the description in another source:
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Peasant
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Re: 8,8 cm PzGr 39 Performance

Post by Peasant » 19 May 2021 11:27

...It should be noted that in many instances the german AP shells do not burst [after penetration] and work like a solid shot.
Image

Photo No.1; unfragmented german 88mm AP shells.

http://btvt.info/3attackdefensemobility ... 4_1944.htm

critical mass
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Re: 8,8 cm PzGr 39 Performance

Post by critical mass » 20 May 2021 09:37

Pay attention to the fact that these tests included >45 deg obliquity vs near cal/D plate, which is beyond the realm of function of the Pzgr.39.

Peasant
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Re: 8,8 cm PzGr 39 Performance

Post by Peasant » 20 May 2021 10:00

critical mass wrote:
20 May 2021 09:37
Pay attention to the fact that these tests included >45 deg obliquity vs near cal/D plate, which is beyond the realm of function of the Pzgr.39.
I'm pretty sure that the mostly undeformed shells we see in this photo were fired at 0-30° obliquity.
I have also seen 5cm german shells left intact after impact against vertical armour:

Image

critical mass
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Re: 8,8 cm PzGr 39 Performance

Post by critical mass » 20 May 2021 14:39

Too many assumptions.

(A) there were VERY FEW normal obliquity tests against the T44. Altough shot by shot data are missing, only four out of fourteen tests were within the proof angle of either 75mm or 88mm Pzgr.39. Thus, the majority of the penetrations should behave exactly as observed. Further, only ONE shell can be charackterized as undamaged in the photo. All shell hits on the front were > proof angle for the Pzgr.39 and the majority of side hits were also at resolved netto compund obliquity >45 deg. The only tests against the side at 30° or 0° yielded such low PSP velocities (487m/s and 595-596m/s) that no damage would have occurred at all to any 88mm or 75mm shell. Without knowing which projectile corresponds to which test, assumptions are uninformed, and thus, not a good advisor. Because they fired life shells, all functioning shells would be highly fragmentated. You wouldn´t have them selected for the photo. This can bias Your perception considerably.
-Also, impacts at high obliquity do render the projectile defunct primarely by forms of base slap, which damages the fuze adaptor. Nose breakage against high obliquity targets is a good feature as it inhibits ricochet.

(B) the 2nd image shows an early KW armor trial, at which time the 5cm Pzgr Gg were in service, primarely. These early ww2 uncapped 5cm shells started to experience break up at ca. 600m/s terminal velocity against a target plate, which they could barely perforate. Those shells would break up against a discriminate target, such as those 75mm plates depicted. Again, You are assuming the projectile was intact, but the fact that the nose is not shown tells me that this is not a likely assumption. In low obliquity impacts the function of a shell is compromised primarely by nose breakage or compression reaching down to the cavity. These shells could not be relied upon to survive this impact in a condition fit to burst.

Yoozername
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Re: 8,8 cm PzGr 39 Performance

Post by Yoozername » 21 May 2021 01:26

Peasant wrote:
20 May 2021 10:00
critical mass wrote:
20 May 2021 09:37
Pay attention to the fact that these tests included >45 deg obliquity vs near cal/D plate, which is beyond the realm of function of the Pzgr.39.
I'm pretty sure that the mostly undeformed shells we see in this photo were fired at 0-30° obliquity.
I have also seen 5cm german shells left intact after impact against vertical armour:

Image
I have read CM say that 7,5 cm Pzgr 39 fragment on a few occasions. I find the notion that 17 grams of HE is going to do much more than blow the tracer/fuse back out of its thread hole to be doubtful. I would not be surprised if it would be helped by actual cracking/etc., from the penetration event (but still being a tight enough containment vessel to affect a high order detonation). Perhaps the actual amount of fragments (OK counting fuze/tracer) might be statistically no more than 4 or 5. That is, if the cap has been destructed completely on the exterior of the armor. i recall that post war interrogation of the German industry by the British claimed that the Germans thought that amount of explosive, and the penetration event (of course), would be enough to disable the crew. basically, being in a closed AFV, and having that explosion, is detrimental to hearing as well as a small concussive event (as well as metal flying around inside).

Image

Yoozername
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Re: 8,8 cm PzGr 39 Performance

Post by Yoozername » 21 May 2021 01:45

there are multiple APHE shells stuck in this KV-1 armor

Image

critical mass
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Re: 8,8 cm PzGr 39 Performance

Post by critical mass » 21 May 2021 18:07

Perhaps except for the mantlet hit and another hit on the joint of two armor plates (which constitutes an unfair hits, which should be discarded anyway), It shows a very ductile response of the armor plate, as could be expected from 42S medium hardness RHA.
When a crack reaches the cavity where the HE filling is located, the tight confinement to build up pressure is lost. Thus, explosions can be blind or low order, typically only 1/4 to 1/3 as powerful as high order bursts. Very small fillers ("Zerleger") will not be powerful enough in such conditions to fragment the projectile fully, owing to the quality of steel and wall thickness around the HE.

This is one of the many difficulties in making high quality projectiles. You have to deal with conflicting requirements. The soft but also brittle soviet shell steel made it easier with their high % fillers to fragment in low order bursts. Attached are drawings of the 5cm..
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Yoozername
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Re: 8,8 cm PzGr 39 Performance

Post by Yoozername » 22 May 2021 06:15

I Think I was very clear that I was speaking about 7,5 cm? In any case, I think you are incorrect. Obviously, even larger capacity 5,0 cm 'stuck' AP do not support your 'fragmentation' supposition? Is this a engineering argument? Or an ego thing?

i will be clear...this is a History site. I support that.

ThatZenoGuy
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Re: 8,8 cm PzGr 39 Performance

Post by ThatZenoGuy » 22 May 2021 11:45

critical mass wrote:
21 May 2021 18:07
Perhaps except for the mantlet hit and another hit on the joint of two armor plates (which constitutes an unfair hits, which should be discarded anyway), It shows a very ductile response of the armor plate, as could be expected from 42S medium hardness RHA.
When a crack reaches the cavity where the HE filling is located, the tight confinement to build up pressure is lost. Thus, explosions can be blind or low order, typically only 1/4 to 1/3 as powerful as high order bursts. Very small fillers ("Zerleger") will not be powerful enough in such conditions to fragment the projectile fully, owing to the quality of steel and wall thickness around the HE.

This is one of the many difficulties in making high quality projectiles. You have to deal with conflicting requirements. The soft but also brittle soviet shell steel made it easier with their high % fillers to fragment in low order bursts. Attached are drawings of the 5cm..
That picture interests me, what the heck is a PzGr 42 50mm projectile?

Also I think I've seen a picture referencing a PzGr 44 88mm (?) projectile from one of your posts, what is that? ;v

critical mass
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Re: 8,8 cm PzGr 39 Performance

Post by critical mass » 22 May 2021 13:13

Yoozername wrote:
22 May 2021 06:15
I Think I was very clear that I was speaking about 7,5 cm? In any case, I think you are incorrect. Obviously, even larger capacity 5,0 cm 'stuck' AP do not support your 'fragmentation' supposition? Is this a engineering argument? Or an ego thing?

i will be clear...this is a History site. I support that.
My response was directed to 5cm impacts as referred to the post above by Peasant, which are older model shells. note that these 5cm pzgr. 38 gG and the 5cm Pzgr.39 had the same HE-cavity. Its fairly well established that the 7.5cm old (pre-Pzgr.39) projectile (in particular the 7.5cm K.Gr.Pz. rot) broke up just as bad -if striking a discriminate target, such as a KW-1E or KW-1 mod.42. It is also known what the function of the "Zerleger" is and how it differentiates itselfe from AP-shell.
Last edited by critical mass on 22 May 2021 13:43, edited 3 times in total.

critical mass
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Re: 8,8 cm PzGr 39 Performance

Post by critical mass » 22 May 2021 13:25

ThatZenoGuy wrote:
22 May 2021 11:45

That picture interests me, what the heck is a PzGr 42 50mm projectile?

Also I think I've seen a picture referencing a PzGr 44 88mm (?) projectile from one of your posts, what is that? ;v
Which post? This is not a Pzgr.44. Its a 5cm Pzgr.42. These were developed to improve upon the 5cm Pzgr.39 downrange performance and obliquity performance. First delivery was made in august 1943 with proof trials conducting in septemper yielding these G(D) results:

30 deg series
70mm: 905m/s (sic. unknown if typo)
60mm: 721m/s
50mm: 624-658m/s
40mm: 508m/s
30mm: 407m/s

45 deg series
60mm: MV
50mm: 805m/s
40mm: 670m/s
35mm: 610m/s
30mm: 507m/s

Little improvment had been obtained at 45 deg as compared to the 5cm Pzgr.39...

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