Early APDS

[Mobius]

I've gone back and compared the various figures stated for APDS and found that either the criteria for penetration has changed over the years or the figures are just wrong for each new generation of APDS.

 

For example end of WWII 17pdr APDS is given byWO 291/1143 shows it to penetrate 232mm @0°/1000 yds. The 20 pdr Mk1 is listed at 280mm @0°/1000yds. In the Centurion in Action book the 20pdr Mk1 is listed at 96mm @60°/1000 yds. And the same book lists the 105mm at 126mm @60°/1000 yds.

 

All well in good by a simple ratio the 105mm would penetrate 126/96 * 280 = 367.5mm. But wait! This is the early APDS, L28 or M392 given in places as 240mm@0°/1000m or 280mm@0°/1000m. Zaloga states the M735 penetrates 370mm@0°/1000m and this is in 1978, 20 years after the first APDS. How can this be? What has gone on here?

[DB]

I've gone back and compared the various figures stated for APDS and found that either the criteria for penetration has changed over the years or the figures are just wrong for each new generation of APDS.

 

For example end of WWII 17pdr APDS is given byWO 291/1143 shows it to penetrate 232mm @0°/1000 yds. The 20 pdr Mk1 is listed at 280mm @0°/1000yds.  In the Centurion in Action book the 20pdr Mk1 is listed at 96mm @60°/1000 yds.  And the same book lists the 105mm at 126mm @60°/1000 yds.

 

All well in good by a simple ratio the 105mm would penetrate 126/96 * 280 = 367.5mm. But wait!  This is the early APDS, L28 or M392 given in places as 240mm@0°/1000m or 280mm@0°/1000m. Zaloga states the M735 penetrates 370mm@0°/1000m and this is in 1978,  20 years after the first APDS.  How can this be?  What has gone on here?

167331[/snapback]

 

Hmm.

 

Firstly, I wouldn't want to assume that the relationship between oblique impacts and perpendicular ones was strictly linear. Particularly, I believe that there may be an additional effect with oblique impacts that depends on the diameter of the projectile (something, perhaps, to do with the way a round may break out of the side of the penetration cavity, rather than being forced to carry straight on through the last bit of the inner face linearly?)

 

Secondly, 1000 yds vs. 1000m is a ten percent difference in range (minor effect, probably).

 

Thirdly, unless the books say otherwise, I suspect that it would be unwise to assume that the same specification of armour target was used in each case. This may well be the dominant effect.

 

Of course, it's also possible that the various sources have been estimating the numbers, based on empirical formulae and other educated guesswork. And that some sources are better at guessing than others.

 

David

[John Gillman]

Workig on shot development with Royal Ordnance I discussed this with old APDS designers back in 1983, at the beginning of the CHARM program. Yes the criteria has changed over the years. A number of factors are relevant.

 

Firstly the design of tanks has changed to utiise sloped armour on the front. So the days of Tiger 1 or Churchill presenting big slabs of frontal glacis armour to the enemy in a vertical plane are long gone. So angled plate at 60 degrees was introduced, similar to the glacis angles presented by tanks such as Centurion or T54.

 

Secondly conducting a "plating" trial was becoming very expensive and difficult to source the plate. The plate had to be big enough to hit and of the correct toughness and hardness right the way through, homogeneity which thinner plates tend to exhibit for much less money.

 

The design of APDS also included ballistic caps. These tended to reduce the penetration length as target angle increased. Firing into a vertical target would negate most of the yaw effects and give a better figure for APDS.

 

However, with APFSDS this tendency works the other way if you measure penetration from the start of the hole in the armour, as with a very oblique plate (such as 72 degrees) the first few inches of penetration remove not a lot of target armour but makes a longer hole. But of course you have to be carefull at close range to get a fair strike with less tha one degree of yaw, so quite a few shots have to be repeated, a typical yaw half life being 400 metres.

 

In the early 1980s we seemed to be spending most of our time firing into the deck plates from aircraft carriers. The shere size of the plates made them well suited to V50 and Theta50 trials.

 

For plating trials of DU shot, the cost of disposal of the "red" target has also to be borne in mind. A thinner, more angled target is cheaper to dispose of than a very thick series of blocks.

[Mobius]

Well 0° is still 0° and 280mm is more that 9% than 240mm. While the Centurion/ Squadron book data doesn't agree exactly with the WO data for 60° values: 17pdr 74/65 and 20 pdr 96/75 would mean the 105 would be even greater in WO 1951 standards.

 

The old standard seems to be 20% greater than the new standard.

[gewing]

Well 0° is still 0° and 280mm is more that 9% than 240mm.  While the Centurion/ Squadron book data doesn't agree exactly with the WO data for 60° values: 17pdr 74/65 and 20 pdr 96/75 would mean the 105 would be even greater in WO 1951 standards. 

 

The old standard seems to be 20% greater than the new standard.

167370[/snapback]

 

 

harder steel nowadays?

[JWB]

Slightly OT but what does CHARM mean? Is it an acronym?

[John Gillman]

CHieftain/CHallenger ARMament. It was originally intended to retrofit Chieftain and challenger 1 with the L30, before MOD decided to buy more Challenger2 instead.

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

Thanks Stuart.

 

What amused me working with the armament boys was the constant signing of requisitions for 2 pounder APC shot. It is still used for armour proving, along with smaller quantities of 6 pounder. I was signing requisitions for 2 pounder during my time in Wpns 2 1983-85 and then scrutinising the requisitions 1988-1995. The shot was normally used to test castings for toughness and tendency to crack. Good old ecky-thump tests!

 

John

[jwduquette1]

Yes the criteria has changed over the years. A number of factors are relevant.

167357[/snapback]

 

Can you define what criteria have changed when determining limit velocity? You mentioned V50. How has determination of V50 changed between circa 1970'ish APDS ballistic trials, and circa-1945'ish to 1950'ish ballistic trials of APDS?

 

I'd be interested in a quantitative example rather than qualitative explanation.

[UN-Interested Observer]

Didn't the British fire their tank guns at a higher pressure than other nations, during WW2? I was under the impression that they did so, and thus their guns did not last as long as others'. Perhaps this is the difference between the new and old data results?

[John Gillman]

Can you define what criteria have changed when determining limit velocity?  You mentioned V50.  How has determination of V50 changed between circa 1970'ish APDS ballistic trials, and circa-1945'ish to 1950'ish ballistic trials of APDS? 

 

I'd be interested in a quantitative example rather than qualitative explanation.

167936[/snapback]

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I am not quite sure what extra explanation you are after. But I queried the result of an APFSDS trial against plate at 72 degrees and was assured that the plate angle added about 30mm of apparent penetration compared with firing at a vertical target. So the shot designer was keen to continue firing at the most oblique target he could, as the results appeared better.

[jwduquette1]

I was interested in an example showing how V50 or limit velocity was determined for say 17-pdr APDS back in the 40’s and 50’s. Than I was hoping for another example showing how V50 would have been determined for say 105mm M392 APDS. I would reckon that citing two numerical examples or shot records from past and present would make whatever differences have evolved in V50 determination fairly evident.

 

Actually you can forgo an indepth on 17-pdr -- but I am curious as to what has changed in V50 determination in more modern ballistic trials.

[Paul Lakowski]

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I am not quite sure what extra explanation you are after.  But I queried the result of an APFSDS trial against plate at 72 degrees and was assured that the plate angle added about 30mm of apparent penetration compared with firing at a vertical target.  So the shot designer was keen to continue firing at the most oblique target he could, as the results appeared better.

167985[/snapback]

 

 

Can you determine what size APFSDS they were testing? What diameter etc?

 

I'm surprised the used aircraft carrier deck plate....maybe I shouldn't be. But what years are we speaking about and which carriers?

[jwduquette1]

Aircraft carrier deck armor would have been constructed from either STS or Class-B plate. Either of these armor types should be expected to perform about as well as tank RHA of UTS ~800 to 900Mpa – dependent upon plate thickness.

 

I presume deck armor was used in these trials as the scrap armor was probably cheap and easy to obtain.

[Mobius]

Moving standards makes it a little difficult the effectiveness of WWII weapons used during Korea, Arab-Israeli and other 1950-1968 conflicts compared to modern weapons.

[Guest Mike Steele]

I have a complete 105mm Training APDS if you want photos of all the components, email me.

[jwduquette1]

Mobius:

 

There is no appreciable difference between how V50 was being determined in late WWII and how it was being determined in the 1970’s and 1980’s, or even the 1990’s for that matter A little back ground checking, and research on the subject should confirm this to anyone remotely interested.

 

Regards

[Guest commander]

Can you determine what size APFSDS they were testing? What diameter etc?

 

I'm surprised the used aircraft carrier deck plate....maybe I shouldn't be. But what years are we speaking about and which carriers?

168010[/snapback]

 

We were firing at HMS Ark Royal deck plates in late 70's and were they thick.

[Mobius]

Mobius:

There is no appreciable difference between how V50 was being determined in late WWII and how it was being determined in the 1970’s and 1980’s, or even the 1990’s for that matter A little back ground checking, and research on the subject should confirm this to anyone remotely interested. 

169086[/snapback]

 

Contradictory results might confirm otherwise. That is why I've brought the subject up.

[jwduquette1]

Contradictory results might confirm otherwise.  That is why I've brought the subject up.

169125[/snapback]

 

You need to be careful you are distinguishing between what is meant by V50, and how it is determined, and what is meant by penetration and/or perforation and how they are determined. Penetration or perforation can be defined in a variety of ways – example BL(N), or BL(A) or BL(P) or Critical velocity, etc. BL(N) does not equal BL(A), but V50 for either form of limit velocity is determined by the same methodology. V50 is simply a weighted mean and its determination has not gone through any significant evolution since the mid-1940’s.

Edited May 4, 2005 by jwduquette1

[DB]

You need to be careful you are distinguishing between what is meant by V50, and how it is determined, and what is meant by penetration and/or perforation and how they are determined.  Penetration or perforation can be defined in a variety of ways – example BL(N), or BL(A) or BL(P) or Critical velocity, etc.  BL(N) does not equal BL(A), but V50 for either form of limit velocity is determined by the same methodology. V50 is simply a weighted mean and its determination has not gone through any significant evolution since the mid-1940’s.

170611[/snapback]

 

Presumably "V50" is a 50% probability of penetrating a given target when the impact velocity is is V?

 

If not, a good definition would be useful

 

However, I think you might have misinterpreted John Gillman's comment regarding V50 - I didn't read it as being that the V50 definition had changed, but that required penetration values had changed.

 

David

[jwduquette1]

However, I think you might have misinterpreted John Gillman's comment regarding V50 - I didn't read it as being that the V50 definition had changed, but that required penetration values had changed.

 

David

170896[/snapback]

 

Could be. But I asked several very specific questions early on in the thread in order to get a feel for what "criteria" has changed. V50 determination has not changed between now and the days of 17-pdr APDS. So what specific "criteria" has changed? Can we put a name and definition to this criteria and how its definition differs from typical limit criterion that may have been used during WWII?

 

As far as a definition of V50 -- it is indeed a 50% probability of occurrence. But it is a probability for a specific ballistic limit definition. A complete or incomplete, or effective penetration under BL(A) criteria does not typically constitute a complete or incomplete or effective penetration under a BL(P) criterion. V50 for BL(A) < V50 for BL(P) <= V50 for BL(N)…or BL(N) ~ CV...or Penetration Limit ~ BL(A) …. Or Perforation Limit ~BL(N)….etc

 

If we are to assume that there is a logical disconnect between commonly referenced penetration figures for say 17-pdr APDS when compared with say commonly referenced penetration figures for 105mm M392 APDS, than a definition of terms is required such that what is actually being compared is understood. Moreover, to normalize 17-pdr APDS performance (if this is indeed required) to that of a more modern ballistic limit standard requires that the modern standard be properly defined -- or at the very least provide the proper "name" of the more modern ballistic limit standard such that we can subsequently compare apples with apples.

Edited May 5, 2005 by jwduquette1

[arrow]

All well in good by a simple ratio the 105mm would penetrate 126/96 * 280 = 367.5mm.

167331[/snapback]

 

From a reliable source I got the following perforation data:

 

UTS approx 800 MPa - range 1000m - air density 1.15kg/m3

 

 

84 mm APDS M1 - v1000=1144m/s

 

258mm@0°

198mm@30° (LOS 229mm)

136mm@45 (LOS 192mm)

72mm@60° (LOS 144mm)

 

 

84 mm APDS M3 - v1000=1308m/s

 

287mm@0°

226mm@30° (LOS 261mm)

162mm@45 (LOS 229mm)

92mm@60° (LOS 184mm)

 

 

105mm APDS L28 - v1000=1381m/s

 

250mm@0°

213mm@30° (LOS 246mm)

171mm@45 (LOS 242mm)

117mm@60° (LOS 234mm)

 

Interesting is that the newer L28 has a perforation limit at 0° wich is minor in comparison to the M1 and M2. The improvement of L28 is at oblique targets (45° and greater).

 

Remarkable is the ratio perforation at normal incidence to perforation at oblique impact for example at 60° for the different types:

 

M1 : 1.79

M2 : 1.56

L28 : 1.07

 

for information - long rod penetrator: 0.86

 

Mobius, your simple ratio is too simple!!!

 

Regards

[DB]

From a reliable source I got the following perforation data:

 

UTS approx 800 MPa - range 1000m - air density 1.15kg/m3

 

[snip]

 

Remarkable is the ratio perforation at normal incidence to perforation at oblique impact for example at 60° for the different types:

 

M1 :  1.79

M2 :  1.56

L28 : 1.07

 

for information - long rod penetrator: 0.86

 

Mobius, your simple ratio is too simple!!!

 

Regards

171215[/snapback]

 

Very interesting data. I would suggest that given the relatively small difference in v1000 between M2 and L28 that one would perhaps gain some insight if one knew the geometries of the rounds involved.

 

Evolution is an interesting thing, don't you think?

 

David

[jwduquette1]

Hi Willi:

 

Thanks for posting the additional data on 20-pdr and 105mm L28 APDS.

 

I wonder if you can provide some additional insight into possible application of the Lanz-Odermatt Equation toward low aspect ratio penetrators – ala first and second generation APDS. I have been looking over the performance of short rod perforation data for sometime now. I can’t reconcile in my own mind why low aspect ratio rods seemingly under perform relative to early (low aspect ratio) APDS projectiles.

 

For example: Considering British 17-pdr APDS vs. monolithic RHA @ 0-degrees, UTS = 800MPa.

 

The approximate geometry of the 17-pdr’s tungsten-carbide core is:

L ~122mm

D ~38mm

 

I have assumed density of the 17-pdr core to be ~15000 to 15500-kg/m^3. For the purposes of my calculations I have used 15500-kg/m^3.

 

I have estimated velocity Drop for 17-pdr APDS to be Approx:

Mv = 1197m/s

1000m = 1062m/s

2000m = 942m/s

 

The attached figure represents normalized perforation for 17-pdr APDS vs. perforation predicted by The Lanz-Odermatt Equation. The 17-pdr perforation data is based upon British War Office figures.

 

It is very encouraging that the Lanz-Odermatt Perforation Curve parallels the British War Office perforation curve. However, there is of course a rather large offset between the two curves. Can I assume that conversion from nominal rod length (L) to effective rod length (Lw) for low aspect ratio rods is at the heart of the perforation curve offset. Perhaps Lw = L – 0.4D or some such thing? Or is there something else going on here?

 

Best Regards

Jeff

 

 

Edited May 6, 2005 by jwduquette1

[Mobius]

From a reliable source I got the following perforation data:

 

Mobius, your simple ratio is too simple!!!

 

171215[/snapback]

 

Intersting data arrow.

The WO didn't publish data in meters during the 50s did they?

 

One thing is the early 105mm L28 APDS was suppose to have serious problems with oblique hits. An improved round had be introduced to fix this problem. But this data shows that it was pretty darn good. Unless this is the improved round.