APDS Shatter Failure Ranges

[rexford]

The British report, EFFECT OF IMPACT AND VELOCITY, listed the results of APDS testing for shatter velocity, which was found to vary with angle.

Firing test data at Isigny, France (found on Mycenius site) and in Thomas Jentz' books for 17 pounder APDS against Panther and Tiger armor resulted in the following conclusions:

1. tests against Tiger 82mm and 102mm armor exactly followed the shatter failure limits set in the EFFECT OF IMPACT AND VELOCITY report

2. while the British report predicted that all hits on the 57° Panther glacis would fail from 150 to 950 meters, 2 of 17 fair hits penetrated between 200 and 800 yards.

The following ranges represent target range intervals where all 17 pdr APDS hits are predicted to fail at the given compound angle:

0 degrees.....none

5.............0-200m

10............0-350m

15............150-950m

20............300-1100m

25............500-1300m

30............650-1450m

35............750-1550m

40............800-1600m

45............750-1550m

50............600-1400m

55............300-1100m

60............0-700m

When 17 pounder APDS strikes the Tiger II turret front head-on, the compound angle is 10° and the hits should penetrate normally beyond 350m. However, if the APDS strikes the turret front at 11° from armor facing the compound angle is 15° and hits fail from 150 to 950 meters.

When 17 pounder APDS struck the 82mm Tiger side armor at a 50° angle and 3511 fps, the hit failed. But when the rounds struck 82mm Tiger armor at the same angle but 3131 fps, it succeeded.

The bottom line is that theory and practice show that APDS had a tendency to fail against the evry targets is was designed to combat, Tigers and Panthers and Hetzers (tests which support theory used 67mm to 102mm armor thicknesses).

[Andrew H.]

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

When 17 pounder APDS strikes the Tiger II turret front head-on, the compound angle is 10° and the hits should penetrate normally beyond 350m. However, if the APDS strikes the turret front at 11° from armor facing the compound angle is 15° and hits fail from 150 to 950 meters.

<hr></blockquote>

Thanks for posting this (and all the other stuff you post, of course). I particularly liked the example I quoted above, though, because it's so easy to imagine stuff like this happening in a CM game.

I also sort of like the image of KTII's charging Fireflies to get closer than 200 meters.

I suppose some people might call that "gamey".

[Stuka]

Yes, Yes. Thoroughly crucial and vital information. I often find myself lying in bed at night, unable to sleep for the pondering of such data as this.

Thank you...and thank you again.

[rexford]

I actually did wake up early one morning and saw that I must convert the velocity and angle data to a failure range interval as a function of angle.

Luckily I sleep with a slide rule by my bed, mostly for cases where the calculator batteries run dry but it works so quiet and well. So I was able to work through the basics of my post without those noisy calculator clicking keys that may wake the others.

And no, I do not wear a slide rule on my belt. Having the rule by my bed, in case of an emergency or wonderful insight that demands instant action, is more than enough security for me.

[JonS]

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

0 degrees.....none

5.............0-200m

10............0-350m

15............150-950m

20............300-1100m

25............500-1300m

30............650-1450m

35............750-1550m

40............800-1600m

45............750-1550m

50............600-1400m

55............300-1100m

60............0-700m<hr></blockquote>

Makes an interesting graph. Looks like maybe a glitch at 15°?

Regards

JonS

[rexford]

If the posted table is what occurred on the battlefield, 17 pdr APDS would not penetrate the Panther glacis or nose on more than an occasional basis at 300m to 1100m. And the Tiger 25° nose armor would beat back APDS hits at 500-1300m.

The Tiger driver plate (10°) could survive 17 pdr APDS at 0-300m.

6 pdr APDS would fail against Tiger front armor at:

350-850m against 25° nose

0-250m against 10° driver plate

The curves are not symmetrical so the 15° results do not match up with higher angle stats.

[c3k]

Rexford,

Thank you. Your research and data is very interesting. I never heard of "shatter gap" before. Let us know when you finally publish all this.

Regards,

Ken

[Dittohead]

It would be nice to know how much of this information Rexford has provided actually has made it into or will be added into the game.

[jshandorf]

I sure could have used this in my tourney game against Jarmo. He put a 57mm Tungsten round through the front of my Panther at 800 meters or so.

Bastard.

Jeff

[JonS]

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

The curves are not symmetrical so the 15° results do not match up with higher angle stats.<hr></blockquote>

Yes, I understand that. What I was getting at is that in two otherwise smooth curves, at 15° for the max there is a spike. If this value were around 800-850 rather than 950m, then the curve would be smooth throughout.

Obviously I don't have access to your data or calculations. I'm merely making an observation based on what I do have - the results. And IMHO the results look odd for the max at 15°.

Shrug. Just my opinion

Regards

JonS

[rexford]

It is always good to keep checking results when they look odd to others. Thanks for continuing to bring up the 15° shatter results.

The critical shatter velocity at 15° is 3528 fps, and the max velocity for shatter failure appears to be 10% higher, or 3881 fps.

17 pounder APDS velocity is 3528 fps at 950m, and is 3881 fps at 150m, based on our estimates.

The 10° shatter velocity range is associated with 3792 fps to 4171 fps, which covers from 0m through 350m.

20° shatter occurs at 3472 through 3819 fps, which corresponds to the 300m to 1100m range interval.

[rexford]

The following is a technical discussion of how much faith can be placed in the tungsten ammo shatter failure predictions. Don't mortgage the house and bet the money on the theory being 100% correct.

-----------------------------------------------

The presented theory on tungsten shatter gap is supported by firing test data against Tiger and Panther, 2 of 17 hits by 17 pounder APDS on Panther glacis at 200 to 800 yards succeed at Isigny, France (8/43) even though most should have succeeded. See page 103 in the book, WW II BALLISTICS: Armor and Gunnery, by L. Bird and R. Livingston, for identification of 17 pdr APDS hits on Tiger that fail despite abundant penetration capability.

U.S. firing tests during WW II showed that steel was not an adequate material for high velocity HVAP ammo because it tended to shatter at velocities approaching and exceeding 3500 fps, even on 0° hits.

Tungsten was chosen for small, high speed carrier based projectiles because it had the ability to hold together at velocities in the 3300 to 4000 fps range. But tungsten will shatter on 0° hits when the impact forces become too high.

We did some additional research on 17 pounder APDS against the Panthers at Isigny. The armor thickness might be assumed to be 82.5mm and the actual glacis impact angle was about 57.3° due to ground slope. The armor would present 252mm vertical equivalent resistance.

The following table presents "penetration/armor resistance" ratio's at the Isigny ranges, estimated penetration probability and actual results (range in yards, assumed standard deviation for penetration probability is 4%):

RANGE..PEN/ARMOR RATIO..PEN.%..ACTUAL PEN.RATIO

200....1.08.............98%.....1-in-3

300....1.06.............94%.....0-in-3

400....1.04.............84%.....1-in-6

600....1.008............58%.....0-in-2

700....0.988............38%.....0-in-2

800....0.972............24%.....0-in-1

The theory predicts all failures beyond 117m till 920m. At Isigny, minimum range for shatter failure appears to be about 200m (ranges in table are in yards), and even then one success occurs at 400 yards against a good quality Panther glacis.

The theory does not hold as well as it did in Tiger case, where all hits within estimated velocity range for failure failed, and hits above the range succeeded. What the Panther analysis presented above suggests is that the shatter range for tungsten ammo may not be an "all or nothing" situation, but reduces the penetration probability from an average of 90% over the 200-400 yard interval to 17%.

The effect of projectile yaw is another consideration, since WW II APDS accuracy was uneven and could be due to uneven shed of the sabot or unbalanced placement of the core in the round. Were the APDS failures against Tiger and Panther due to a combination of shatter tendency at higher velocities and striking armor at odd flight angles (nose and tail of projectile were not aligned along the flight path)?

The APDS rounds fired at the Isigny Panther were very inaccurate, and would entirely miss the Panther on occasion. A similar situation occurred when U.S. forces fired APDS from a 57mm anti-tank gun at captured Panthers, an inability to hit the target was noted.

The above discussion suggests that the tungsten shatter theory be applied cautiously and with full recognition of the fact that it might fall on its face when APDS performs in proper fashion (goes where it is aimed).

[Redwolf]

I find the accuracy considerations most interesting. It always stroke me how a round that was losing part of itself after it left the barrel should be as precise as a "whole" round.

[gunnergoz]

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

I find the accuracy considerations most interesting. It always stroke me how a round that was losing part of itself after it left the barrel should be as precise as a "whole" round.<hr></blockquote>

I agree that it's interesting, Redwolf. It is apparent that a ton of research dollars went into this precise question in the post-war years. Todays sabot rounds are highly accurate of course. I'd love to hear more about sabot engineering development history...Rexford, any sources to point us to? (Thanks Rexford, BTW )

[rexford]

During Isigny tests (August 1944 in France) with 17 pounder APDS, 3 shots out of 7 at 800 yards failed to hit a Panther front target aspect, and while the shots were aimed at the glacis only one of four hits struck the glacis.

At 800 yards, APDS aims at and hits glacis once in seven shots (1-in-7)

At 700 yards, APDS hits glacis 2-in-7 tries

At 600 yards, APDS hits glacis 3-in-4 tries

At 400 yards, APDS hits glacis 8-in-11 shots

At 300 yards, APDS hits glacis 4-in-8 shots

At 200 yards, APDS hits glacis 3-in-5 shots

All told 17 pounder APDS aims at glacis 42 times and hits 21, for 50%

17 pounder APCBC aims at glacis and hits 9-in-9 shots (100%)

76mm HVAP aims at and hits glacis 14-in-18 shots (78%)

17 pounder APCBC aims at Panther nose (small target partially obscured by ground folds) and hits 4-in-6 (67%)

76mm HVAP aims at and hits Panther nose on 4-in-6 (67%)

The 17 pounder guns were fired by two superior British enlisted gunners, the U.S. 76mm by two officers with considerable test firing experience.

On July 10, 1944, First U.S. Army tested 17 pounder APDS at Balleroy and obtained two penetrations of the Panther glacis on two hits at 700 yards. This result is contrary to the predictions for tungsten round shatter and also suggests much better penetration performance than obtained at Isigny.

Lorrin