About the debate of the gun accuracy in CMBN,I extract some discussion of lorrin bird

[Erwin.Rommel]

FIRST ROUND ACCURACY OF GERMAN GUNS

The following hit percentages are taken from German ballistic tables

(capped AP) and refer to the case where the range is known to a

stationary 2m high by 2.5m wide target, and the random dispersion is

doubled to model battlefield conditions:

RANGE..50L60...75L48...75L70...88L56...88L71

500m........100.....100.....100......100.....100

1000m.... ...95......66......97.......93......85

1500m........68......33......72.......74......61

2000m................16......49.......50......43

2500m.................8......29.......31......34

3000m.................5......18.......19......25

Relative dispersion in the above table follows some unexpected

patterns, with 75L70 being less scatter prone than 88L56 out to

1000m, but after that range 88L56 is slightly more accurate in terms

of repeatability. With regard to 88L71, the scatter pattern is more

diffuse than 75L70 and 88L56 at ranges out to 2000m but then attains

a superior performance at 2500m which increases with range.

German data for their use of the captured Russian 76.2mm L51.5 gun

showed dispersion patterns similar to the 75L48 when APCBC was

fired., with similar hit percentages with a known range.

The 50L60 and 88L71 data applies to both the tank gun and towed

weapons, while the 88L56 figures are limited to the tank gun. Review

of data for the 88mm L56 Flak suggests that that weapon may have

possessed greater dispersion than the tank gun.

The marked inferiority of 75L48 scatter to the other guns is

unexpected., since the 75L43 was used to knock-out T34’s at ranges

above 1000m. It would be interesting to see if 75mm L46 Pak 40

dispersion had the same general values as the 75L48, which came along

at a later date.

It has been written that the introduction of the 50mm Pak in Africa

greatly extended the range of direct fire combat for tank and anti-

tank gun units, and the relatively close scatter pattern and

excellent gun sight quality for that weapon would be superior to the

2 pdr anti-tank gun in both respects.

Using the German figures for doubled random dispersion and assuming

an average range estimate error of 25% with a bell shaped error

distribution (typical results for average crew, based on British and

American firing trials), the following first round hit percentages

were computed against a stationary 2m high by 2.5m wide target:

FIRST ROUND HIT %

RANGE...50L60...75L48...75L70...88L56...88L71

500m...........81......75.....88.......79.....94

800m...........36......34.....51.......39.....61

1100m..........17......15.....28.......21.....34

1400m...........9.......7.....16.......12.....19

Muzzle velocities are 835 m/s for 50L60, 750 m/s for 75L48, 935 m/s

for 75L70, 780 m/s for 88L56 and 1000 m/s for 88L71. All rounds APCBC

except APC for 50L60

A 2m x 2.5m target size was used by the Germans as a reasonable model

for the front view of a typical target tank, which simplified the

calculations. Those dimensions simplify the complex variations in

target width with height (T34 turret front is narrower than hull and

has sloping sides, T34 hull width varies with height, etc.), and

probably assume that ground rolls and folds blocked out some of the

lower tank area.

The above stated estimates for first round hit percentage probably

represent the high side of what would be expected from average troops

in battle, since “nervous and/or fatigue” origin errors were not

considered during the calculations. Under the stress of combat,

people can forget intermediate steps and see things on the gun sight

that are not there. Discussions on the AFV News forum site have

brought out the possibility that unquantifiable human errors may

account for a good share of the reported misses at “sure thing”

ranges.

Regarding second shot corrections after misses, the Germans advised

that bracketing should be used at ranges above 1200m using 200m

increments below 2000m and 400m above that distance. At or below

1200m, "fire for effect" corrections to the initial shot would be

made using various methods that would result in a more accurate

change in shot placement than adding or subtracting 200m.

An American gunnery manual for the Sherman indicates that bracketing

is to be used at ranges over 1000 yards due to gun sight limitations

which restrict the crew ability to make fine adjustments to the gun

setting.