APDS SLOPE EFFECTS

[rexford]

Latest CM patch adds tungsten slope effects, which work out to 5.00 multiplier for 60 degree hits.

American test data extrapolated to 60 degrees is about 4.25 for 76 HVAP, 4.50 for 90 HVAP.

British data for 17 Pounder APDS on John Salt site gives 3.54 slope multiplier at 60 degrees, same figure as CM for 30 degrees.

Logically, one might expect APDS to have lower slope effects than HVAP, no energy loss due to carrier.

CM data works out to about 4.20 slope multiplier at 55 degrees for APDS, so Panther glacis resists like 80 x .85 x 4.20, or 286mm at vertical. No 17 pounder APDS penetration at any range.

This result is in conflict with many actual tests, Balleroy test shoot against captured tanks results in two 17 pounder APDS penetrations against Panther glacis at 700 yards on two hits. Isigny test has one penetration of Panther glacis at 200 and 400 yards with APDS where glacis is at about 57 degrees.

John Salt data is in closer agreement with test firing results, the 55 degree slope multiplier for APDS is 2.75 if 60 degrees is 3.54.

The above slope effects are for "good" APDS that flies straight and true, if sabot pieces discard at different times than the flight path is skewed and both accuracy and penetration/slope effect suffer.

Our booklet will provide 17 pounder APDS data that provides additional support for lower slope effects, including analysis of tests against Tiger E 100mm and 80mm armor at oblique angles.

[Old Major]

*scratches head*

[:USERNAME:]

Is this booklet going to be written in this same convoluted ramble?

I have been following (somewhat) your pamphlet/booklet announcements and have some trouble understanding your points or even what you are saying. I cant imagine what the new guys are thinking..

You seem like some excited runner from the frontlines bearing such important news that you cant gush it out coherently.

Breath. Think. write.

Lewis

PS The british had solved the problem of sabots hanging onto the AP tungsten. It was theorized to be the reason for the innaccuracy of APDS. But there was still innaccuracies afterward. The americans also thought this was the issue with thier APDS (which was not produced in time for WWII).

The XRay photos proved the british right. The real issue is the centering of the tungsten round in the sabot shoes and the whole thing being balanced. Any inbalance will manifest itself (in a rifled weapon) in a barrel 'jump' (think of the mismatched weight 'corkscrewing' up the barrel).

I believe the brits put a weight at the end of the fireflys/achilles barrel. Whether they knew it or not, this would have helped with solving the jump problem.

The brits also had the tungsten sheathed in some sort of 'non-discarding' metal. This helped the sloped armor penetration problem.

Anyway. Please stop perpetuating this sabot 'issue' myth. I hope your booklet makes it clear what you 'know' as fact and what you are theorizing/conjecturing.

good day.

[This message has been edited by :USERNAME: (edited 03-04-2001).]

[Ari Maenpaa]

It would serve us all to get those slope multipliers as close to the real thing as possible. That kind of historical accuracy increases the game's playing value immensely.

Originally posted by :USERNAME::

PS The british had solved the problem of sabots hanging onto the AP tungsten. It was theorized to be the reason for the innaccuracy of APDS. But there was still innaccuracies afterward. The americans also thought this was the issue with thier APDS (which was not produced in time for WWII).

The XRay photos proved the british right. The real issue is the centering of the tungsten round in the sabot shoes and the whole thing being balanced. Any inbalance will manifest itself (in a rifled weapon) in a barrel 'jump' (think of the mismatched weight 'corkscrewing' up the barrel).

I believe the brits put a weight at the end of the fireflys/achilles barrel. Whether they knew it or not, this would have helped with solving the jump problem.

The brits also had the tungsten sheathed in some sort of 'non-discarding' metal. This helped the sloped armor penetration problem.

Nice to have new info about the APDS-issue. Could you, Lewis, also give more precise dates for those "fixes" the Brits used with APDS-rounds? Did they have an effect on actual WW2 combat? Are they applicable to CM? I got the impression that most things you wrote were applied only after the war.

Rexford provided weblinks to the actual wartime test results where the 17-pdr APDS was discovered to be extremely inaccurate. Something as convincing would be good to see. So how well did the Brits deal with the inaccuracy issue DURING the war?

Ari

[John Kettler]

rexford,

That's very interesting to know. I'd also like to see more on those APDS fixes Lewis described. News to me.

With the above addressed, I wonder if I might borrow you and your ammo grog buddies and ask you to take a look at the 75mm Too Expensive? thread which just got bumped? There is a dispute over blast ratings for 75mm FA vs 81mm

mortar. CM rates the 75mm as having the substantially greater blast. Given even first order fill fraction differences between the two, I fail to see how the mortar round comes up short. Please help. We need detailed data on explosive fills.

Thanks!

John Kettler

[rexford]

John Salt site on hit probability has test results comparing 17 Pounder APCBC with APDS, APDS is alot less accurate in many tests.

Jentz' books give firing test results for APDS against Tiger which suggest that something is very wrong when they are analyzed, as they are in our booklet. Rounds that have 40% more penetration than armor resistance fail to pierce, while another shot at same equivalent armor succeeds.

Jentz states that APDS was not particularly accurate. Everything that we have been able to find shows that APDS was inconsistent.

CM should revise APDS slope effects to agree with John Salt site data, and introduce random decrease of accuracy that is associated with radical reduction in penetration. Many sources state that they had trouble hitting a target with APDS, let alone hitting a particular area.

And then the Panther glacis armor quality should be randomized to range from 1.00 to 0.80, with 1/3 to 1/2 of tanks at 1.00.

And only the Panther glacis has armor quality below 1.00.

The above revisions would improve modeling of WW II armor resistance and APDS penetration/accuracy.

Booklet Philosophy:

The booklet is aimed at folks who are interested in estimating penetration ranges or seeing what is involved, and would like improved slope effects, flaw multipliers, penetration data and other factors (cast deficiency to rolled armor, high hardness effects, etc.). Slope effects are different for AP, APC/APCBC and APBC, as well as APDS and HVAP.

CM uses some of the data we have, alot more will be published in booklet.

When 17 pounder APCBC hits Panther glacis, medium flaw armor quality is 0.93, not 0.85.

Booklet will present armor on tanks, plate by plate, along with identification of cast, flawed, face-hardened and high hardness areas that need multipliers.

Spaced and layered armor will be identified and methods offered so single plate resistance can be calculated. Churchill with 88 front hull in CM has 178mm total layered armor around hull MG and sloped lower front hull, while CM lists 0 degree angle and 88mm.

The booklet can be used on many levels, simplest use is taking slope effect curves and penetration data and just using that.

Another level is using cast deficiency to rolled, and looking at flaws.

Soviet armor analysis HAS to use high hardness factors to make any sense. There will be a one page table where high hardness armor thickness is compared to projectile diameter and the multiplier is found, or one can use the graphed curve.

The booklet is written in a form that first presents the basic data needed to use the curves and tables, and then there will be 20 or so appendices that contain detailed studies that may be important to a reader. Analysis of Kubinka tests against Panther glacis is one appendix, firing tests against Panther another, and firing tests againt Tiger another.

If the DeMarre equation is potentially useful, there will be a basic introduction and then an appendix that has analysis of DeMarre estimating errors, compares DeMarre to National Physical Equation estimates and also includes data on American ammo penetration drop off at high velocity with tie-in to shatter gap.

Shatter gap will be in book, U.S. 76mm APCBC will fail to penetrate 100mm driver plate on Tiger from about 50 yards to 1000 yards, with 0 degree lateral shot angle.

We have not seen listings of face-hardened penetration data for Allied and Russian ammo anywhere (including CM), and that pen. data is extremely important because most panzers carried that armor type. Tiger II carried some face-hardened armor, so did many Panthers. So our booklet will be valuable because it provides something that is not readily available elsewhere.

That is why we put the booklet together, because it addresses stuff that isn't anywhere else in a consistent format.

Readers can use the booklet on whatever level they wish and should not feel that they "have" to tackle everything, or that the book loses value because parts of it interest some but not all.

If all this sounds too complex wait until the initial reviews are published and then decide. The booklet is written in a "to the point" style.

[:USERNAME:]

Originally posted by Ari Maenpaa:

Nice to have new info about the APDS-issue. Could you, Lewis, also give more precise dates for those "fixes" the Brits used with APDS-rounds? Did they have an effect on actual WW2 combat? Are they applicable to CM? I got the impression that most things you wrote were applied only after the war.

I am just aware of the fact that the british knew this phenomena to be the real underlying cause of the innaccuracies. The US designers confirmed that the sabots were leaving as they should. It was then discovered that the problem was developed within the barrel not after!

I dont know for a fact that the brits put an inertial weight on the end of the 17 lbr for barrels for a fix. If you look at Steel Infernos B&W pictures, you will see an example of an achilles with some sort of collar wrapped around the barrel right before the muzzle brake. It could be some sort of counter balance but would also (perhaps serendipitously) stop the barrel jerk I described above.

The only other way to solve this is to have strict quality control where the penetrators are spun at a very high RPM to make sure they are balanced. The shoes on the sabots would have to be matched by weight and the penetrator sitting perfectly between them.

But the US design and brit technology sharing was all late war stuff. Alot of the programs were dropped flat at the end of the war.

All of this is because the APDS is being fired from a rifled gun. The preferred way to do it nowadays is to use a smooth bore and then its pretty much a non-issue.

[Paul Lakowski]

I gather from talking to Andrew Jaremkow , that the APDS problems were solved by the Canadians after the war , infact apparently much of the design of the 20lb and 105 APDS owes it origines to Canadian research. I have 1969 Canadian research papers on the possible development of a DU APDS which also reviews tungsten carbide and alloy penetration.

The shatter gap is evident in the work and the researchers show how its 'reboud effect'as striking velocity increases can be controlled by the shape of the nose.

Extensive radio flash imagery show that any deviation of the projectile while penetrating occurs within the first 40-50 microseconds ...or so. This is important because that means the round 'turns or doesn't turn' before the main body of the projectile digs into the armor plate .

This is why I believe its all in the projectile nose sharpness and tip design.

[rexford]

Thanks for good info on APDS issues.

Same stability-of-flight problems popped up with 115mm APFSDS when it was shot out of smoothbore gun. Trajectory could become unstable during 1973 War, and Israeli's reported that T62 rounds could strike ground sideways.

Discarding sabot ammo appears to have teething problems. 76mm HVAP had smallest dispersion of any WW II projectile, and Brits reported that HVAP didn't decrease accuracy of APCBC ammo shots that followed HVAP use, while APDS use would impact accuracy of APCBC shots that followed. We have British report on this, obtained from Bovington.

APDS slope effects in CM are too high and should be revised downward. See John Salt site penetration listings for proper figures. For verification of Salt figures, examine penetration ranges for 17 pounder APDS against Panther glacis (Isigny is good example as it references Balleroy), and compare to CM results.

We analyzed 17 Pdr APDS tests against Tiger 100mm and 80mm armor in Jentz books, and Salt slope effects were verified.

[rexford]

Previous posts on this site referred to studies showing that sabot shed was not the problem with accuracy/penetration, it was off-center sabot placement. And that weight on Achilles barrel helped solve APDS problems.

Would appreciate references for these statements.

Thanks.

[rexford]

Oooops!

Meant to say off-center core placement in previous post.

Insufficient sleep will do you in every time.

[:USERNAME:]

Do I win a free pamphelet if I tell you?

[JunoReactor]

*Taps at his head, pointing towards the thread*

This thread is crazy.

[This message has been edited by JunoReactor (edited 03-06-2001).]

[rexford]

Came across some material on WW II APDS, associated accuracy problems with disturbances caused by sabot shedding, did not add anything else.

Achilles added weight to barrel for reasons other than APDS accuracy.

[Claus B]

Originally posted by :USERNAME::

I dont know for a fact that the brits put an inertial weight on the end of the 17 lbr for barrels for a fix. If you look at Steel Infernos B&W pictures, you will see an example of an achilles with some sort of collar wrapped around the barrel right before the muzzle brake. It could be some sort of counter balance but would also (perhaps serendipitously) stop the barrel jerk I described above.

The barrel counterweight was only found on the 17pdr Mk V used in the SP 17pdr M10 (a.k.a. "Achilles"). The towed AT-guns did not have it, nor did the Firefly or the Challenger.

The M10 had a massive weight on the rear of the turret in order to balance the original 3" gun. The 17pdr had a different weight distribution and the barrel weight was added to compensate for the turret weight. Compensating for the compensation!

Claus B

[rexford]

Asked for help on other sites regarding APDS problem causes, here is what I received from Conall(references to follow):

1. APDS disrupted by muzzle brake interference with discarding sabots

2. Uneven discarding of sabots (YEAH! I is vindicated)

3. Bad ammo production during early stages

4. Poor type of discarding sabot on British APDS, different from model that eventually lead to uniform performance

5. Gun sight wasn't designed for APDS ranging

CM really needs to model APDS inconsistency in terms of accuracy/penetration. Anything less is just not realistic. Once in a while APDS works like design, other times it doesn't. Our booklet will present enough data to estimate good/bad percentages.

And while they are at it, change the tungsten slope effects so they are in line with published test results (60 degree slope multipliers of 3.5 for APDS, 4.4 for HVAP), instead of home-brew concoction of 5.0 in CM.

If CM crew is dedicated to quality, the inconsistent quality and true slope effect of APDS should be addressed.

[Mattias]

I guess BTS has a lot of things on their mind but I certainly hope they are taking notes.

One could possibly argue that at some point enough is enough, but it seems to me that BTS, at least in the past, have been willing to go the extra mile.

Hopefully they'll continue down that path.

M.

[Simon Fox]

The question I have to keep asking here is when. I don't dispute that British testing clearly demonstrates that at least the 17pdr APDS was substantially less accurate. The testing also seems to show that proper calibration of the gunsight and experience with firing the round ameliorates this innaccuracy to certain extent. The real question is when these problem were identified (quite early I suspect since the gun itself had been around for ages), what steps were taken to rectify them, when these were implemented and how effective they were.

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

"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"

[rexford]

I'am sure BTS will eventually model APDS with random variations from poor to good, even if only two states.

Based on high velocity of round, APDS should be much more accurate than 17 pounder APCBC. At Isigny, APDS hits target area about 55% of time, 17 pounder about 85%. APDS fails to even hit target at ranges where errors in gun sight use should still land shot on target.

Penetration tests against Tiger show about 40% of APDS doesn't penetrate what it should, probably a yaw related problem.

Other American tests note inability to hit target on many shots.

All of this suggests at least 40% of APDS rounds with reduced accuracy and almost no penetration capability due to yaw angle (hitting something with a sideways moving round just doesn't cut it).

Subject to further study, it might be reasonable to assume that 40% to 50% of APDS is near useless, due to yaw. We have enough data to refine this figure but don't have time at present.

Conall's info suggests problems that couldn't be addressed without redesigning APDS and removing muzzle brakes, which didnt occur. WRG wargame rules for miniatures made a statement that accurate/effective APDS was a post-WW II development.

Most interesting tungsten use was Littlejohn adaptor, placed on 2 pounder and 37mm light tanks/armored cars, that theoretically allowed penetration of Tiger front hull at close range. I believe Littlejohn used squeeze bore teck-nolo-gee, and no other rounds could be fired with adaptor on gun (was there squeezebore HE?).

Can CM tanks and armo cars use Littlejohn adaptor?

Further threats to poor old PzKpfw IVH, little tanks and armored cars running around shooting tungsten rounds with over 100mm penetration at close range. Wonder if a penetration would be noted if round didn't hit anyone, due to small size and fact that tungsten rounds may break up during penetration (or so I read somewhere, although test firing against Tiger in Jentz shows APDS holding together after it penetrates 80mm armor).

[Conall]

Originally posted by Simon Fox:

The testing also seems to show that proper calibration of the gunsight

Simon,

I suggest you take a look through the gunsights which were issued to British tanks equipped with the 17pdr during WW2. Whether you look at the:

No. 43 x3 L Mk.I (Sherman C only - Firefly)

No. 43 x3 ML Mk.I (1st 23 A30 Challengers only)

No. 43 x3 ML Mk.3 (A30 Challenger)

No. 43 x3 ML Mk.3/1 (Sherman C - Firefly)

you will see one common feature. None of these sights have any markings/graticules/range scales for APDS ammunition. Therefore your suggestion that proper calibration of the gunsight would improve APDS accuracy falls a little flat. I think the testing you are refering to concerns APCBC rounds in use with the AT gun & then the tank mounted 17pdr - the problem was one of the sight becoming rapidly misaligned due to the heavy recoil (a problem not unique to the 17pdr).

I agree that experience with APDS would help but in my opinion only marginally at best & would vary from the experience of one individual to another (therefore a little hard to teach, standardise & even model for a computer game/simulation).

I hope this helps a little - more to follow with references tomorrow(ish).

Regards,

Conall

[John Kelly]

Rexford,

I notice that you use a particular modifier to calculate effective armor thickness based on slope. How does the modifier change when you consider both armor slope and angle of attack? For instance if a tank superstructure is 80 mm with a 60 degree slope, you use one number, but what happens when this superstructure is hit from an oblique angle of say...45 degrees? John

[Simon Fox]

Therefore your suggestion that proper calibration of the gunsight would improve APDS accuracy falls a little flat.

It wasn't my suggestion, it was what the WO document I was reading seemed to suggest. Not personally having experience firing 17pdrs in tank or AT tank mode I preferred to take some notice of the conclusions of those who did, however wrong they may be. Me peering through a gunsight and then drawing conclusions about the accuracy of various rounds would be as effective as sticking my head up my arse and diagnosing intestinal polyps.

My inclination is that the 17pdr APDS rounds didn't get used much anyway since the APCBC was pretty good. The 6pdr was a different matter but then we have a different gun and round.

A Littlejohn adapter on the Daimler 2pdr would be really cool, hehe. Anyone know if they ever made and issued a 2pdr HE round? Even experimentally?

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

"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"

[rexford]

The booklet we are going to publish goes into the problem of compound angles, which is what is required when a vertical angle is combined with a lateral angle.

Panther 55 degree glacis might be hit at 15 degrees from straight-ahead, which represents a 56.4 degree compound angle. Slope effects are then computed on the basis of T/D and compound angle.

It turns out that the steeper the vertical slope the less effect from lateral angles.

Advanced Squad Leader rulebook does not have any HE for 2 pounder gun. What is really interesting is that 28/20 German squeezebore anti-tank gun does have an HE shell. 20mm HE sounds real intimidating, like German 20mm APCR. Tungsten core must have been less than 1/2 inch wide.

Brits say that littlejohn cores for 37mm and 2 pounder were around 18mm wide, which is around 3/4 inch.

37mm gun on Stuart had HE.

Advanced Squad Leader doesn't appear to have Littlejohn squeezebore adaptors for 37mm and 2 pounder guns, so they did miss some "important" things.

57mm Soviet anti-tank gun, alias "the hunter", fired AP and APBC at over 3000 fps, which we believe is responsible for many recorded close range hits on Tiger with few penetrations. At 3000 fps and over, 57mm rounds with low nose hardness are bound to shatter on 80mm and 100mm thick armor (ye olde shatter gap). U.S. studies predict that square nose rounds, like Soviet 57mm APBC, are even more prone to shatter failure than normal AP, since nose stresses are greater on low angle hits against armor when T/D is greater than 1.00.

[rexford]

If none of the gunsights used with APDS is calibrated for the ammo, this makes APDS even less accurate than it might be when the sabots work as designed!!!!!!!!!!!!!!

APDS is looking less and less accurate.

Would British tanks want to use APDS instead of APCBC?

1. APCBC can't dent Tiger II turret front, APDS can and should pierce on most hits (IF it works properly)

2. APCBC may shatter against Tiger mantlet or fail to penetrate very thick areas, APDS would have alot less trouble, if any

3. APCBC cannot penetrate Panther or JagdPanther glacis at point blank, APDS that works like it should can, and out to 700 yards or more.

APDS designed to attack and penetrate thick armor that APCBC self destructs against. Even if half the APDS is poor and doesn't work well, half a chance is better than none. With regard to gun elevation, if APCBC at 2900 fps requires 5 mils elevation, APDS at nearly 4000 fps could be assumed to be a certain percentage of APCBC angle.

Was reading about the many ways British camouflaged or tried to hide Firefly barrel so Germans wouldn't pick out tank for rapid elimination. Like phoney muzzle brakes halfway down barrel and the like. How come Germans in CM pick out my Fireflies right away at all sorts of ranges and volley fire at the 17 pounder tank.

A Firefly at 700m range, facing directly at a Panther, isn't that different from a 75mm Sherman. If Germans can spot 17 pounder tanks that quick then APDS becomes a moot point when British attack.

[Jeff Duquette]

ooophs double post

[This message has been edited by Jeff Duquette (edited 03-09-2001).]