My Last Thread on 17 pdr APDS Inaccuracy

[rexford]

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.

[Bruceov]

What does apds stand for; what does apcbc stand for

[flamingknives]

Go to the FAQ thread for descriptions of acronyms.

In this case:

APDS = Armour Piercing, Discarding Sabot

A sub-calibre shot where the casing that holds it in the barrel separates as it leaves the barrel. This improves the velocity, and hence the penetration characteristics.

APCBC = Armour Piecing, Capped, Ballistic Cap.

A full calibre shot, with a soft metal cap that supports the hardened tip, reducing shatter. This improves performance against hard and face-hardened armour. The Cap is typically quite blunt, so the ballistic cap is a light 'windscreen' added to improve the aerodynamics of the shell.

[Michael Emrys]

Originally posted by flamingknives:

A full calibre shot, with a soft metal cap that supports the hardened tip, reducing shatter. This improves performance against hard and face-hardened armour.

Is it not also the case that the soft, blunt cap reduces riccochets against highly sloped armor? Or was my source just talking through his hat on that one?

Michael

[flamingknives]

Originally posted by Michael Emrys:

</font><blockquote>quote:</font><hr />Originally posted by flamingknives:

A full calibre shot, with a soft metal cap that supports the hardened tip, reducing shatter. This improves performance against hard and face-hardened armour.

Is it not also the case that the soft, blunt cap reduces riccochets against highly sloped armor? Or was my source just talking through his hat on that one?

Michael </font>

[rexford]

Originally posted by Michael Emrys:

</font><blockquote>quote:</font><hr />Originally posted by flamingknives:

A full calibre shot, with a soft metal cap that supports the hardened tip, reducing shatter. This improves performance against hard and face-hardened armour.

Is it not also the case that the soft, blunt cap reduces riccochets against highly sloped armor? Or was my source just talking through his hat on that one?

Michael </font>

[LT. James Cater]

Thanks for the info.

But whatever the hell Fireflys are using whenever i play usually works really well.

I mean they are DEADLY!!!!

Rarely have one of their shots been deflected. I'm just glad that it can be knocked out at long range.

[rexford]

Originally posted by LT. James Cater:

Thanks for the info.

But whatever the hell Fireflys are using whenever i play usually works really well.

I mean they are DEADLY!!!!

Rarely have one of their shots been deflected. I'm just glad that it can be knocked out at long range.

One of the things that gives Fireflies an extra boost in CMBO is the 85% armor quality on the front glacis of a Panther. The game applied one 0.85 quality factor for all rounds, but our work applied a 0.95 multiplier for 17 pdr APCBC hits on the glacis and something similar for APDS.

And CMBO does not model the erratic accuracy and failure to penetrate that was often found with WW II APDS (6 and 17 pdr APDS).