17 pdr APDS Failures Against "Easy Armor"

[rexford]

Reports of Allied firing tests against captured Panthers and Tigers suggest that 17 pdr APDS hits were failing when the penetration was significantly greater than the effective resistance. The following lists identify the cases from two series of firing trials where over-penetrating 17 pdr APDS hits failed to defeat the armor, with angled hits converted to an equivalent vertical resistance.

Jentz’ Germany’s Tiger Tanks, Tiger I & II

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17 pdr APDS attack on Tiger Armor Fails

82mm @ 50° => 180mm/0°, round hits at 3511 fps with 237mm/0° penetration

102mm @ 48° =>207mm/0°, hit at 3437 fps with 229mm/0°

102mm @ 48° =>207mm/0°, hit at 3215 fps with 209mm/0°

102mm @ 41° =>163mm/0°, hit at 3427 fps with 229mm/0°

102mm @ 41° =>163mm/0°, hit at 3602 fps with 245mm/0°

Isigny Firing Trials

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17 pdr APDS attack on Panther Armor Fails (82mm glacis armor is assumed)

82mm/57.1° =>249mm/0°, 2 hits at 600 yards with 3700 fps and 255mm/0° penetration (glacis #2)

82mm/57.6° =>255mm/0°, 2 hits at 400 yards with 3781 fps and 263mm/0° (glacis #1)

82mm/57.1° =>249mm/0°, 3 hits at 400 yards with 3781 fps and 263mm/0° (glacis #2)

82mm/57.1° =>249mm/0°, 1 hit at 300 yards with 3823 fps and 267mm/0° (glacis #2)

82mm/57.1° =>249mm/0°, 1 hit at 200 yards with 3865 fps and 271mm/0° (glacis #2)

82mm/56.9° =>246mm/0°, 1 hit at 200 yards with 3865 fps and 271mm/0° (glacis #3)

One explanation for the failures is flight instability due to yaw created by uneven shedding of the sabot petals, which was one of the suspected causes of accuracy problems.

Another failure explanation is tungsten core shatter gap, where firing trials revealed that hits which exceeded a certain velocity at each angle shattered, resulting in the need for significant over-penetration for the hit to succeed.

The tungsten core shatter gap curve identified the following velocities where shatter would occur and the penetration needed for success would be higher than the effective resistance:

0 degrees, 4093 fps

10 degrees, 3757 fps

20 degrees, 3458 fps

30 degrees, 3290 fps

40 degrees, 3234 fps (limited firing tests)

45 degrees, 3252 fps (limited firing tests)

50 degrees, 3290 fps (limited firing tests)

55 degrees, 3364 fps (limited firing tests)

60 degrees, 3589 fps (limited firing tests)

The problem with the shatter gap theory is that the Panther failures turned into success in several cases when the penetration was raised to about 12% above the effective resistance, while the trials against Tiger show failures with 30% to 50% more penetration than effective resistance. This suggests that the most likely cause of the 17 pdr APDS failures against Tiger and Panther were due to excessive yaw.

[Mr. Tittles]

I would expect this to be an intermittant problem if it is due to yaw. The reason being that yaw would not be constant and in some cases non-existant. I assume the APDS did not have any fin stabilization and was just a pointed bolt of sorts?

Did this ammo have any way of transfering the spin imparted on the sabots to the projectile? In other words, was there slip between the discarding parts and the tungsten core?

Also, is there any information as afr as the failures leaving gouges? If they are gouging the armor, would this be indicative of shattering?

[flamingknives]

APDS never has fins and is always spin-stabilised*. If it had fins, it would be APFSDS. Slip rings, AFAIK, were only introduced for APFSDS fired from rifled barrels. Interestingly, a slight spin improves the accuracy of fin stabilised projectiles, as it counters the effect of eccentricities in the projectiles.

*Of course, someone will be along to decry my use of such absolutes

[John D Salt]

Originally posted by flamingknives:

APDS never has fins and is always spin-stabilised*.

[snips]

*Of course, someone will be along to decry my use of such absolutes

This evening, Mr. Picky was unavailable for comment.

Back to you in the studio, Brian.

[rexford]

Test report on the Mycenius site includes a report of U.S. use of 57mm APDS during tests against captured Panther tanks:

"5) 57mm Gun, M1

a) APC, M86 will penetrate the sides and rear of the 'Panther' Tank at 1500 yards.

Sabot fails to penetrate front glacis slope plate and gun shield at 200 yards. Due to difficulty experienced in obtaining hits no conclusion as to the effectiveness of this ammunition was reached."

Given the 100mm thickness of the curved Panther mantlet and the 200 yard range, there is a possibility that the failure of 57mm APDS was due to excessive yaw.

There is another good AFV News thread on APDS ammo at:

http://www.activevr.com/afv/cgi_bin/web-bbs/webbbs_config.pl/read/53369

[rexford]

Here are Derek Ward's findings (from AFV News site) on the likely cause (yaw) of 17 pdr APDS accuracy and penetration problems, based on WW II research reports:

"Well I got them in and digested them - alas they are still NOFORN and US Contractor/DOD only after all the years. I can not publish the data here but I will publish the report titles and the conclusions I have drawn from them without giving away the farm.

The first is 'Yaw of a 3"/57mm sabot fired from the British 17pdr' Dated June 1943 - Author HP Hitchcock Memorandum Report 171. Projectile stability of this experimental round was rated as satisfactory. This was a 57mm APC core fired as trial ammunition. Yaw was comparable to standard APCBC in most cases.

In this regard there appears nothing particularly peculiar about the 17pdr as a gun that would confirm or deny gas blowby of the projectile in the data. A limited number of rounds were fired, and I note nothing unusual in their performance expect for one problematical sabot separation.

Thse second report is 'Exterior Ballistics Of The British APDS Shot For The 17pdr Gun' - Same author - BRL Memorandum Number 325 - Dated 5 Sept 1944.

This report deals with the production ammunition, and gives a detailed break down of the shot components by weight/diameter/etc. The trial was run in a standard manner for the time - yaw screens coupled to rather crude electric switches. It is obvious from this data that projectile yaw is an issue.

There were also some problems with APDS components hitting these components and destroying them during firing.

Reviewing the data I can tell everyone that the degree of yaw is sufficient to result in marked penetration/velocity loss, certainly enough yaw to degrade penetration by the amount Lorrin has seen in some of the other test data (IMHO).

The problem is obviously one of sabot/base plate separation, with resulting velocity degradation and loss of penetration on impact (angle of impact).

There was a problem noted with the ammunition that might have been a quality control issue or lack of attention at the storage depot prior to delivery to the US. It would have had an impact on the performance of the ammunition in test given the nature of the problem, and I was suprised to see it in ammunition this recently off a production line.

If that were typical of production ammunition then ammunition quality/storage/preparation is also a definate culprit...and could have acted in synergy to make the demonstrated problem worse.

The quality isssue is such that it could have varied between lots and/or storage conditions.

In summary - two major culprits - projectile yaw (a definate major symptom) and an issue with the ammunition itself - not pertaining to design - but to premature degradation. (demonstrated in the test ammunition, probably at least one of the causes??).

Typical of all lots? I dont know...but it would have also played a role in this issue if it were.

(hint: yes it did relate to the sabot and base plate)

Given the yaw demonstrated with trial ammunition in the first report vs the production ammo in report 2, I don't think its a fault of the gun...its definately the ammunition...its definately a yaw issue...and if the test ammunition is an indicator then there is possible quality problem resulting in premature ageing.

Regards All

Derek"

Good work on his part.