WW II, a British focus





Rheinmetall-Borsig, Unterluss

This firm made the 7.5 cm. tank gun. For proving, the gun was mounted on a fixed mounting with a normal recoil mechanism. Kleinschmidt, from memory, gave the following figures for dispersion on a vertical target.

At 1000 metres : 50 per cent zone, 1 metre at most
At 1500 : same angular dispersion.

The gun to gun variation was small. The Heereswaffenamt probably fired these guns on a tank mounting, but Kleinschmidt did not know of any figures for the dispersion when obtained. No jump determinations of any description were made at Unterluss.

When the 7.5 cm. L/48 gun was rigidly mounted (on Jagd Panzer 38 t), the first figures for dispersion were unusually large. It was found, however, that there was large wear at the muzzle of the particular gun being used. When some two or three calibres length were cut off from the muzzle end, the dispersion, obtained was as good as with the same design of gun mounted normally with the usual recoil system.

The 38 cm. rocket projector mounted on a Tiger chassis gave the following dispersion against a vertical target.

At 1000 m 100 per-cent zone, 1˝ to 2 per cent of range
6000 m 100 per-cent zone, 3 to 4 per cent of range.

Range tables for this equipment were said to be with GSI (Tech), H.Q. B.A.O.R.

Krupp, Essen (personnel evacuated to Kettwig)

Dr. Dihrberg said that specification required that 50 per cent of shots should fall within a 50 cm. square on a vertical target at 1000 metres range. Dispersion was checked for tank guns, with 10 round groups, at ranges varying from 500 to 3000 metres.

Jump varies slightly from gun to gun, but for range table purposes the results from a single gun are taken, since the variation is very slight. Droop is considered a constant for all guns to a given design.

Rheinmetall-Borsig. Dusseldorf

Muller stated that the accuracy required of tank guns was laid down by the Heereswaffenamt, but neither he nor Zimmer could state from memory what the requirements were. The design department of Rheinmetall-Borsig was moved in 1943 from Dusseldorf to Leipzig, and due to air attack there, it was subsequently moved again to the suburbs of Leipzig. Ludwig, Hermann and Banck of this department may have some details on this matter of accuracy. All were possibly at Dillenburg, near Wetzlar. (Braun of Unterluss thought that Hermann and Banck were at Heidenheim).

Muller did not know the required tolerances between bore and shot. He considered that there was no gun to gun variation in jump (i.e. for a given design) provided the propellant charge was standard. Droop was disregarded, because tank guns were considered to be too short and stiff for droop to be important.

Krupp’s Main Range, Meppen

For guns required to be very accurate (eg. tank and anti-tank guns), about 95 per cent of rounds fell within a rectangle 60 cm. high and 30 cm. wide on a vertical target at 1,000 metres. It was stated that the dispersion for line is less than for height. The ratio of lateral to vertical dispersion remains substantially constant at all "flat-trajectory" ranges for any gun. The angular dispersion also remains nearly constant with range in the flat-trajectory region.

Herr Hengefeld, interviewed at his house in Meppen, gave the following figures for bore tolerances, which were required throughout the length of the bore

7.5 cm gun : High 7.51 cm. Low 7.50 cm.
8.8 cm. gun : High 8.81 cm. Low 8.80 cm.

The shoulders of all shot were finished by centerless grinding.