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[rexford]

I accidentally posted on 17 pdr APDS on the wrong forum, please delete.

John Salt's Snippets can be used to determine the relative constant aim dispersion of 17 pdr APCBC and APDS, and the previous finding that APDS has about twice the scatter is about right.

WO 291/238 gives the calculated first shot hit probabilities for several guns and ammo, assuming a 1000 yard target range and a standard error of 250 yards (25% average error, where the assumed errors range from 0% to over 75% and follow a bell-shaped distribution).

17 pdr APCBC is estimated to have a 15% first shot hit chance against a 2' high target, while the APDS is 19%. However, due to the flatter trajectory of APDS compared to APCBC the APDS advantage should be higher.

Using the Jurens-Okun trajectory program, the impact of the range estimation error was identified and the 1000 yard standard dispersions were calculated as:

17 pdr APCBC 68% of scatter within 0.43m of aim point

17 pdr APDS 68% of scatter within 0.95m of aim point

The random scatter of APDS is about 2.2 times the APCBC figure.

Even if 17 pdr APDS was fired at a 2m high target at 1000 yards and the range estimate/gun elevation were perfectly on, about one-third of the shots would miss due to random scatter.

The British WO report notes that the wide scatter of 17 pdr APDS makes accurate second shot correction difficult, since the first shot might be based on an accurate range estimate but the wide dispersion could cause a high shot that suggests a long estimate.

One interesting note from the WO report is that the service infantry range finder is expected to have a standard range estimate error of 25 yards at 1000 yards, where 68% of the estimates will be equal to or less than 25 yards and 32% will be greater than 25 yards. The average range finder error at 1000 yards is 2.5%, compared to 25% for a man making a visual estimate.

There is a large amount of information in John Salt's Snippets and in the Isigny and First Army firing test reports from the Mycenius site which conclusively show that APDS was very erratic in flight and not very accurate.