APDS SLOPE EFFECTS

[Claus B]

Originally posted by Paul Lakowski:

Claus you say they looked similar, did that include cutaway of the interior of the penetrator? I had a pic some where that shows 17lb with a ballistic cap over the penetrator under the windscreen, does the pics your looking at show the same?

They look externally similar, including all the groves in the projectile.

There is a cross-sectin drawing that shows the part of the projectile that travels to the target to consist of:

1. Shot. The actual tungsten penetrator

2. Front Sheath. A mild steel sheath covering the front part of the projectile and interlocks with the rear sheath about 1/3 from the bottom of the shot. Purpose is to function "as a shield or cover to protect the core."

3. Nose cap. A duralumin "spacer" that keeps the shot properly aligned within the front sheath.

4. Rear sheath. Covers the lower 1/3 of the shot and fits tightly to it. It interlocks with the front sheath. The tracer is fixed to the bottom of the rear sheath

5. Tracer. Fixed to the bottom of the rear sheath and protrudes into a cavity in the bottom of the sabot.

What would the purpose be of a ballistic cap *under* the windscreen (front sheath)?

Claus B

[Paul Lakowski]

Its supposed to allow for better slanted penetration.

[Claus B]

Originally posted by Paul Lakowski:

Its supposed to allow for better slanted penetration.

I thought ballistic caps (as in apcBC) was there solely for the purpose of aerodynamics. Are you thinking of an armour piercing cap (apCbc)?

I dont think the sheath would survive the impact long enough to have any effect, being of mild steel as it is.

Claus B

[rexford]

APDS penetration and accuracy could also dramatically decrease from 200 to 800 yards, as indicated during the Isigny tests.

[Paul Lakowski]

Originally posted by Claus B:

I thought ballistic caps (as in apcBC) was there solely for the purpose of aerodynamics. Are you thinking of an armour piercing cap (apCbc)?

I dont think the sheath would survive the impact long enough to have any effect, being of mild steel as it is.

Claus B

Ballistic Research refers to 'Ballistic Caps' as the penetrating cap and the other cap as the 'Windscreen'

[Simon Fox]

Connall wrote

This appears to have been very successful & anecdotally was reported to have been a better balanced turret than the original 75mm Sherman, which in turn improved the smoothness & ease of the turret traverse.

So how does this impact on the Firefly turret traverse speed? I note that in CM it was recently downgraded to medium in comparison to the 75mm Shermans fast.

Claus B wrote

However, in the real world, 17pdr APDS appears to have been so inaccurate that shooting at anything more than 1000 yards away would be a waste of ammo. I assume that this means that the chances of hitting any part of the tank was so small that it was an excercise in futility to try it.

Claus is correct here. The 1000yds limitation is definitely a guideline arising out of accuracy trials, penetration not being a significant factor in these recommendations. I beleive, however, that your "futility" comment is a little excessive. My understanding is that the British established their range criteria on the basis of at least a 50% chance of a hit with any round (including) the first, against a hull-down target. Maybe Conall could expound further on the criteria issue.

On another subject, Claus may know the date the Achilles was phased in, I thought it may be a bit earlier than the CM date. It was such an popular conversion being a much better "fit" with the vehicle than the 3in (other considerations aside) that I thought that the conversion program was rushed ahead.

[rexford]

British report WO 291/762 describes the result of a comparative firing test with 6 pounder APCBC and APDS against a 2' x 5' target (hulldown Panther). Churchill IV was used.

See the John Salt site on hit probability.

APCBC outperformed APDS beyond 500 yards in terms of hit %:

500 yards, 74% for both ammo types

800 yards, 50% for DS, 73% for APCBC

1000 yards, 37% for DS, 62% for APCBC

1500 yards, 20% for DS, 42% for APCBC

British found that dispersion and jump varied so much from one gun to another during APDS use that a single conversion factor did not apply to all tanks when they used the APCBC gun sight settings (with 17 pounder, multiply estimated range by 0.5 when firing APDS and using APCBC gun sight scale).

If individual gun characteristics were used to construct range conversions with APCBC gun sight settings, APDS accuracy might be improved by about 60%.

Despite probable absence of muzzle brake on Churchill IV, APDS was still less accurate than APCBC.

John Salt site also provides report that recommends 800 yard max range for APDS, based on 50% first shot accuracy against hulldown tanks. In difficult situations, such as when facing a Tiger II at 1200m with no where to run or hide, 17 pounder armed tanks might resort to APDS in the hope that they had decent ammo, since APDS might penetrate the turret front and APCBC definitely would not.

So APDS performance is inconsistent during 6 pounder trials despite probable absence of muzzle brake, and accuracy is less than APCBC at ranges below 1000m. This points to problems may that go beyond muzzle brakes and involve petal shed/exhaust gas interference.

APDS accuracy is, as has been theorized, a truly random event that requires random selection of accuracy and penetration figures. Listening CM?

[rexford]

During the firing tests described in previous post, it was found that two Churchills had such awful accuracy with 6 pounder they could not be included in overall statistics for comparing APDS with APCBC.

This suggests a new thread.

[rexford]

The APCBC/APDS comparison in my first post on 6 pdr firing tests compared 5 tank APCBC to 3 tank APDS (best 3 against best 3 plus worst 2).

Following is comparison of best 3 tanks for each ammo, % refers to overall hit percentage against 2' x 5' target (Panther turret):

500 yards

89% APCBC, 74% APDS

800 yards

84% APCBC, 50% APDS

1000 yards

81% APCBC, 37% APDS

1500 yards

62% APCBC, 20% APDS

APCBC is much more accurate than APDS for best 3 tanks.

[Claus B]

Originally posted by Paul Lakowski:

Ballistic Research refers to 'Ballistic Caps' as the penetrating cap and the other cap as the 'Windscreen'

Now, aint that sweet!

So when the ballistic researches are testing what the users, the manuals and the textbooks describe as "Armour Piercing Capped Ballistic Capped (APCBC)" they are referring to it as "Armour Piercing Ballistic Capped with Windscreen" (APBCWS

That would certainly help screw up communications!

Does this apply to modern terminology only or does the terminology (windscreen vs ballistic cap) go back to WWII?

Anyway, neither cap is present on the 17pdr APDS Mk 2 round. Only the protective sheath and the nose pad holding the shot in place within the sheath.

Claus B

[Claus B]

Originally posted by Simon Fox:

The 1000yds limitation is definitely a guideline arising out of accuracy trials, penetration not being a significant factor in these recommendations. I beleive, however, that your "futility" comment is a little excessive. My understanding is that the British established their range criteria on the basis of at least a 50% chance of a hit with any round (including) the first, against a hull-down target.

I am with you - I just wanted to make the point stick

Originally posted by Simon Fox:

On another subject, Claus may know the date the Achilles was phased in, I thought it may be a bit earlier than the CM date. It was such an popular conversion being a much better "fit" with the vehicle than the 3in (other considerations aside) that I thought that the conversion program was rushed ahead.

Off my head,

the British had recieved the SP 3" M10 back in 1943. 17pdr conversions began in February 1944 and first combat was on June 6th 1944.

I am not shure when the 3" M10 first saw service with the British in Italy, but I am positive that some were around in early 1944.

The 3" M10 continued in service with UK and Commonwealth troops well into 1945, probably to wars end. When the last Canadian troops relocated from Italy in February 1945, they took their 3" M10s with them to Holland. They were immidiatly turned in and replaced by the SP 17pdr M10.

Claus B

[Simon Fox]

Thanks Claus that was my inclination having read a few regimental diaries and accounts of M10s with 17pdrs in Normandy. If you have any hard data I would appreciate it. If there perchance ever is another patch for CM it would be nice if the availability matched the historical case.

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

"Stand to your glasses steady,

This world is a world of lies,

Here's a toast to the dead already,

And here's to the next man to die."

-hymn of the "Double Reds"

[Paul Lakowski]

Originally posted by Claus B:

Now, aint that sweet!

So when the ballistic researches are testing what the users, the manuals and the textbooks describe as "Armour Piercing Capped Ballistic Capped (APCBC)" they are referring to it as "Armour Piercing Ballistic Capped with Windscreen" (APBCWS

That would certainly help screw up communications!

Does this apply to modern terminology only or does the terminology (windscreen vs ballistic cap) go back to WWII?

Anyway, neither cap is present on the 17pdr APDS Mk 2 round. Only the protective sheath and the nose pad holding the shot in place within the sheath.

Claus B

OK I'll have to see if I can copy that pic I saw a while back....I'm sure it was a 17Lb with a ballistic cap...we'll see.

[Claus B]

Originally posted by Simon Fox:

Thanks Claus that was my inclination having read a few regimental diaries and accounts of M10s with 17pdrs in Normandy. If you have any hard data I would appreciate it. If there perchance ever is another patch for CM it would be nice if the availability matched the historical case.

One of the best sources on this is Dick Harleys articles in AFV News Vol. 28/1, Vol. 29/2 and Vol. 27/3.

Harley has done quite extensive research in the war diaries of different British A/Tk Regiments and batteries that served both in Italy and Normandy.

As an example, "Y" Battery of 21st A/Tk embarked for Normandy on June 21st with six 3" M10 and six 17pdr M10. "Q" battery recieved their first three 17pdr M10s on May 19th and three more on May 21st. They went to Normandy on June 20th. The "Q" battery war diary even gives names and serial numbers of both their 3" M10 and 17pdr M10s and Harley quotes them all.

Another source is Bastins "The Norfolk Yeomanry in Peace and War" which deals with the 65 A/Tk Regt. They served with the 7th Armoured Division. Bastin is also very precise about the issue of 3" M10s and the subsequent change to 17pdr M10. On May 9th 1944, 260th Battery moved to Brentwood where they changed their 3" M10s for 17pdr M10s. This resulted in a lot of work as the new vehicles had to be waterproofed, the guns zeroed etc. They landed in Normandy between June 7th and June 12th.

Interestingly, 260th Battery was attached to Brigadier Hindes Brigade Group when it moved towards Villers-Bocage on June 12th and it seems likely that the "self propelled anti-tank guns" mentioned in both German and British sources about the battle for Villers-Bocage were indeed M10s, probably the 17pdr M10s of 260th Battery. There is even a picture of an abandoned 17pdr M10 with at least 4 penetrations being examined by a German tanker. The picture is allegedly taken on June 13th in the Villers-Bocage area in which case the 260th battery is the only possible owner. The vehicle has serial S2378? and is a late production M10.

Claus B

[Conall]

Originally posted by Paul Lakowski:

OK I'll have to see if I can copy that pic I saw a while back....I'm sure it was a 17Lb with a ballistic cap...we'll see.

Paul,

Are you referring to the picture I sent you a awhile ago - if so I resent it to you. If you haven't got it just give me a shout & I'll resend it.

Regards,

Conall

[rexford]

John Salt site ending in salt5 has comparative accuracy tests where 6 and 17 pounder fired APCBC and APDS (WO 291/324).

6 pdr APDS is less accurate than APCBC, 17 pdr APDS is more accurate.

This continues the APDS story of inconsistent behavior.

It is also notable that APDS accuracy is not improved by zeroing gun to APDS performance as opposed to APCBC, as British had theorized.

[Simon Fox]

I assume you have WO 291/324 in that shed of yours since you seem to have additional information to that provided by John Salt in his brief extract/precis of that document.

Does the document base it's analysis on firing trials rather than expected error or estimation? What is the date of the document?

It certainly seems strange that it disagrees with WO 291/1263, "Firing Trials, 17pdr Sherman." which is also summarised by Salt.

[Paul Lakowski]

Originally posted by Conall:

Paul,

Are you referring to the picture I sent you a awhile ago - if so I resent it to you. If you haven't got it just give me a shout & I'll resend it.

Regards,

Conall

No Conall. Two years ago Andrew Jaremkow and I were exhamining modern APFSDS projectiles [ no suprise there], I made the observation that in ballistic research most 'scale models' used as test include a hemispherical nose design. Andrew produced a ton of pics that did show German APFSDS and 105 APDS with rounded noses. I found a book 'Ammunition for the modern land battle field' that included cutaways drawings of 120mm APDS 17 lb APDS and 6 Lb, and as I recall the 6 Lb was the only one that didn't have a rounded nose.

In long rod penetration studies sharp nosed penetrators take a longer route through slanted armor[ 60-70°] as one would expect but only about 1.1 times the LOS.Rounded nosed APFSDS take a shorter route through the armor, but not by much and @ 45° it takes a slightly longer route [ 1.05 times].

Flat tipped penetrators are the best taking only 0.8 times the LOS penetration route through the armor @ 60-70°. Thus most APFSDS penetrate up to 20% more than the LOS penetration value if they feature a flat nose.[M-829 series, British L23 Israeli and now Chinese APFSDS as well].

The long and short of it is that Anderson Jr [ probably the world leader in research] discovered that the effects of the nose disappear after the projectile has penetrated 2 rod diameters or about 40-50 microseconds and I found APDS studies from the 60s that show this in steel and Tungsten APDS.

Every thing about WW-II and alot on modern penetration depends on that nose design.

[rexford]

Simon Fox:

The point of APDS-vs-APCBC firing trials is that APDS is inconsistent, it may be less accurate than APCBC in one set of tests and then perform better in another test.

This has been the point of all the information posted on the subject, APDS cannot be modeled with one set of accuracy or penetration stats because it is all over the place. Sometimes it works well, sometimes it doesn't.

No contradiction here.

The test data I referenced is firing test data, not calculated or estimated.

[Simon Fox]

Originally posted by rexford:

Simon Fox:

The point of APDS-vs-APCBC firing trials is that APDS is inconsistent, it may be less accurate than APCBC in one set of tests and then perform better in another test.

This has been the point of all the information posted on the subject, APDS cannot be modeled with one set of accuracy or penetration stats because it is all over the place. Sometimes it works well, sometimes it doesn't.

No contradiction here.

The test data I referenced is firing test data, not calculated or estimated.

Actually I agree with you that APDS demonstrated inconsistent performance, this is very clear and seemingly without dispute. What I don't agree with is your mangling of the language which merely obscures the point you are trying to make. If study A says APDS is more accurate than APCBC and study B says APDS is less accurate than APCBC then study A disagrees (the word I used) with study B, the results of the studies are inconsistent with each other and they contradict one another.

I think you are missing the intriguing point here. If the performance of APDS is inconsistent then that should show up as intra-trial variation which would lower the results of any particular firing trial given that a sufficiently large sample of rounds were used. This certainly appears to be the case for most of the trials discussed here. Therefore the poor accuracy results for APDS in those trials seems to be due to round to round inconsistency which leads to an overall poor mean performance.

When different trials disagree the issues are different. Then the contradictory results are due to either: (A)differences in the methodologies employed to perform the tests or analyse the results or both; ( differences between the rounds used. In the case of B the most likely explanation is not intra batch performance but inter batch performance. That would relate to a manufacturing issue rather than a fundamental design problem.

Therefore you may have two distinct phenomena occurring and since you don't have a chronology of these tests things get a little cloudy.

Clear as mud?

Good

[rexford]

Simon Fox:

Long before your last post, we looked at the two APDS-vs-APCBC accuracy trials with different results, examined the causes of APDS variation that would be common to both tests, considered an estimate of total rounds fired, and realized that different lots were probably involved : one lot was good, one was bad.

The above explanation is essentially the same as the bureaucratic and "clear as mud" concepts you just espoused.

Since production inconsistencies were likely to be the main difference between the two tests, it backed up our theory that APDS was, as a general rule, inconsistent. Conall's response's on APDS have suggested that quality control and production quality could vary, representing a primary difference in two test results.

By the way, I'am a licensed professional engineer and have done ALOT of work on statistical sampling, quality control and confidence intervals relating to airport pavement condition studies. Regarding your startling analysis of APDS inconsistency between two tests, it isn't.

[rexford]

Prior to posting the data on the second test (APDS-vs-APCBC accuracy), we looked at the factors that might vary between tests, and realized it was manufacturing differences.

As a licensed professional engineer with mucho experience doing statistical studies and sampling, as well as quality control, it was obvious that many factors canceled out and lot quality was the primary factor.

With regard to Simon Fox' intriguing and startling findings on why the two tests on John Salt site pointed to basic inconsistencies in APDS manufacturing, they aren't.

We figured out a long time ago one test had a good lot, another a bad lot.

We've been saying inconsistency was a basic element of APDS accuracy and penetration for a long time.

[rexford]

Bump!

[rexford]

Is chronology a factor in why one test shows poor APDS quality and another doesn't? In other words, did APDS get better with age?

APDS problems appear to be based on alot of gun related problems and some basic manufacturing problems. So three questions arise:

1. were solvable APDS problems identified and addressed prior to war end? Could be yes or no, but no real statements were found that significant improvements transpired before war's end. Anyone with info on this invited to participate.

2. is it possible to identify a date when APDS improved, and the percentage of available rounds that benefited, for wargame purposes (probably not)

3. would be it be reasonable to use the same factor for random APDS inconsistency throughout the war (probably)

March, 1945 6 pdr APDS tests are addressed in Jentz book, and results suggest a good percentage of bad ammo.

Yes, we have no dates for the two tests, so our findings are suggestive rather than definite. And there is a 50% chance that APDS-better-than APCBC test occurred earlier than the other test.

APDS is inconsistent on about half the shots, and there is no data as to when any improvements took place during WW II, if any.

If anyone wants to search through WO reports for dates and details, and then search for APDS improvements during WW II and associated details, it would be appreciated.

[Paul Lakowski]

Originally posted by Conall:

Paul,

Are you referring to the picture I sent you a awhile ago - if so I resent it to you. If you haven't got it just give me a shout & I'll resend it.

Regards,

Conall

OK I fianlly got the other 17Lb APDS drawing I was looking for. It looks quite different from the pic that conall sent me, the Sabot looks different and the length looks different too 4:1 length to diameter on Conalls pic and 3.5 :1 on the drawing I have also the tip looks more blunted but theres no cap as in the 105 and 120 APDS.The sheathing looks substancially thicker on my drawing compared to Conalls.Theres very little gap between the inside of the 'windscreen' and the penetrator tip , where as theres more on Conalls pic.

I'll see if I can scan this and I got a website the other day so with any luck I'll get it loaded up soon.

[This message has been edited by Paul Lakowski (edited 03-14-2001).]