a white elefant: the 10.5cm L/70 and derivates

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critical mass
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Location: central Europe

a white elefant: the 10.5cm L/70 and derivates

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Post by critical mass » 01 Sep 2017, 16:43

Probably the most potent, full calibre anti tank gun of ww2.

history:

1941:
preliminary requirements for the gun of LÖWE was to be able to defeat 180mm RHA(80kg/mm² tensile strength) @ 30° and 1000m distance

january 1942:
Turret design of LÖWE ordered.

february 1942:
besides the 10.5cm KWK L/70, WaPrüf investigates the feaability of 12.8cm L/50 and 15cm L/40 turrets for this tank.
10.5cm L/70 is investigated in regard to feasability of installation in VK 4501 (P) and VK 4501 (H) for future upgrade (turret ring diameter: 2000mm)

march 1942:
Krupp is ordered to provide a proof firing installation for both, 10.5cm L/70 KWK and 8.8cm L/71 KWK proof guns

april 1942:
the 12.8cm and 15cm alternatives for further development of LÖWE turret guns are excluded.
WaPrüf ordered gun design for 10.5cm KWK with elevation engine.

May 1942:
turret design drawing developed so far as to provide engeneering drawing.
project with 10.5cm L/70 turret is for the first time called "obsolete".

May/ June 1942:
WaPrüf ordered Krupp to design 10.5cm KWK L/70 and associated equipment and provide engeneering drawings in order of 1500 engeneering days.

July 1942:
Engeneering drawings for cartridges (1 VII 30279) and chamber (1 VII 30260) have been exchanged between manufacturer and WaPrüf. WaPrüf is asked to provide 100 cartridges for the initial proof firing of the gun. Cartridge similar to 12.8cm FLAK 40 acc. to drawing 13 C 6311.

August 1942:
Krupp informs W3 the latest design charackteristics of the 10.5cm L/70 as follows ("Rohrdaten"):
V0: 965m/s
g= 18.0kg [my note: weight of projectile]
ac= 855 mt [my note: recoil forces]
l= 11.4kg [my note: presumably weight of charge]
Jv= 14.7 dm²
Js= 68.0 dm²
pg= 2900 kg/cm²
pa= 3500 kg/cm²
pk= 3600 kg/cm²
r= 3500kg with breechblock and muzzlebreak [my note: presumably weapon weight]

Sept. 1942:
Krupp finalized the engeneering expanses for LÖWE with 535 engeneering days and submits their bill. Project is entirely cancelled.

Decembre 1942:
Wa Prüf 4 ordered at Krupp the manufacture of a proof barrel 10.5cm L/70 with a V0 of 1000m/s.
WaPrüf 1 requires progressive rifling due to high V0. Manufacturer responds that the gun is to be finnished in MAY 1943. Konstant rifling would have hastened the manufacturing of the barrel.

january 1943:
the manufacturer responds that there is no acute interest for the 10.5cm L/70 under manufacture after LÖWE had been dropped and ask for confirmation of the order. Finnishing of the proof barrel was scheduled for MAY 1943.

Krupp responds to WaPrüf 4 the costs for making 50 specimen each for APCBC-HE projectiles of the types 10cm Pzgr rot (drawing 13 C 1415) & 10.5cm Pzgr L/4.3 (drawing AKG 10025, 1057) intended for the 10.5cm L/70. Costs are 250 RM each for the 10cm Pzgr rot and 260RM each for the Pzgr L/4.3.

february 1943:
The present L/70 barrel is under finnishing manufacturing ("befindet sich in der Fertigbearbeitung") and has been designed for two projectile types giving the following performances:

10cm Pzgr rot, weight 15.6kg, V0: 1025m/s
10.5cm Pzgr L/4.3, weight 18.0kg, V0: 965m/s

the manufacturer asked to increase the rifled length from 6950mm (=L/66) to 7220mm (=L/68). With this length, the reviewed new V0 for the 10cm Pzgr rot (15.6kg) is recalculated with V0-new :1075m/s. Altough no data for the heavier 18kg AP projectile are given, the muzzle energy agrees with a V0 of 1000m/s with an 18.0kg heavy projectile.
The barrel is to be finnished and delivered by JUNE 1943.

march 1943:
WaPrüf 4 agreed with the finnishing of the proof barrel for the 10.5cm L/70 as 10.5cm L/70 s.PAK with increased rifled length for the intent to conduct firings ("Fertigstellung und Verwendung als Beschußrohr") -probably of experimental nature.



Some observations.
WaPrüf 4´s reissued order for a 10.5cm L/70 KWK / PAK clearly postdates the cancellation of the LÖWE tank project by several months. Nevertheless, once Wa Prüf4 in decembre 1942 reissued interest in the 10.5cm L/70, Krupp does not hesitate to use the already prepared 10.5cm L/70 gun deign and only slightly adapts the gun to also accept AP at a somehow higher velocity with longer rifled length than the original design.

[II] The penetration graphs in Lilienthalreport 166 for the 10cm Pzgr rot (15.6kg) end at 950m/s. At this velocity, the projectile could defeat 240mm RHA (70-80kg/mm^2 tensile strength) at an obliquity of 60° (= 30° to the perpendicular). Extrapolated from the curve for this projectile, penetration at 1025m/s (original V0) would have been closer to 280mm and with 1075m/s (reviewed V0) closer to 300mm RHA @ 30°, considerably more powerful than any other gun of ww2 (even including 12.8cm PAK 80/ KWK44´s). A performance far beyond to that originally intended for the project.

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