APDS SLOPE EFFECTS

[rexford]

Jentz' Tiger book has some tests where 6 pdr APDS fired against Tiger during 1945. There are a number of cases where penetration is alot larger than armor resistance, which suggests bad trajectory (yaw angle) throws off penetration.

From page 17:

1. 6 pdr APDS should penetrate 127mm at 24 degrees and 3390 fps, it fails against 102mm at 24 degrees.

2. 6 pdr APDS should penetrate 123mm at 30 degrees and 3507 fps, it fails against 82mm at 30 degrees with a Panther track attached.

3. 6 pdr APDS should penetrate 142mm at 24 degrees and 3665 fps, it fails against 102mm at 24 degrees with a Panther track attached.

There are a few more cases that suggest bad APDS ammo trajectory, and this is a March 1945 test. As Conall pointed out, sabots banged against muzzle brake as round left barrel or sabots clung too long on one side, throwing round off its' path. Throw in gun sights that went out of adjustment or didn't have APDS calibration and things keep getting worse.

How many rulesets out there treat WW II APDS as a "hit or miss" (in literal sense) ammo. None that we can find.

In our miniatures rules we throw a dice for APDS, and on about half the rolls the ammo is useless. But like I said in previous post, half a loaf is better than none against Panthers, Tiger II's and JagdPanthers.

To do WW II right, one needs randomizing rolls for APDS usefulness, Panther glacis armor quality, etc.

[Jeff Duquette]

A couple gun sight images for the 17-pdr Conall sent me awhile back (during the big 88mm accuracy thread). It’s always kind of interesting to look at these old optics. Gives you another piece of the puzzle as to what it may have been like to fight in a WWII tank.

Interesting that APDS graticules weren’t provided in the 17-pdr gun sight (and presumably the 6-pdr as well). The difference in mv is quite considerable between APDS and APCBC…1204 m/s and 884 m/s respectively. APDS must have had a much flatter trajectory. Perhaps this would be analogous to a modern MBT GAS in which the loader has HEAT up, but the gunner is using the SABOT gun sight. I think Conall may really be onto to something here.

http://www.geocities.com/tigervib_2000/Crap/17pdr_site1.html

http://www.geocities.com/tigervib_2000/Crap/17pdr_site2.html

[This message has been edited by Jeff Duquette (edited 03-10-2001).]

[rexford]

Computed the gun elevation angles for 17 pounder APCBC and APDS against targets at 500, 800, 1100 and 1400 meters. In all four cases, APDS gun elevation angle is about 55% of APCBC.

If this ratio was known by authorities (good likelihood), and was given to Firefly crews (good chance), crews in field might be able to correct for absence of APDS lines by roughly "halving" APCBC elevation.

This subject does require more info on exactly what was done to properly aim APDS.

[rexford]

Good post Jeff! Showing that scope view really added a missing dimension to the thread.

[rexford]

My just posted posts forgot to belabor the well worn party line: APDS slope effect at 60 degrees is 3.54, not the 5.00 that CM uses. APDS done properly can kill a Panther or JagdPanther thru the glacis at 700 yards or greater, which CM may not be able to duplicate at present.

Good performing APDS is a gem, worth wading thru all the bad sabots and missing gun sight lines and in-the-way muzzle brakes and everything else.

Firefly APDS fans demand better slope effects, reduced dependability and less accurate sabot!!!! This way it's exciting like Las Vegas, where one loses miserably or wins like a million!

[Paul Lakowski]

Originally posted by 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.

OK thats Sqrt of [1/COS² 55°+ 1/COS² 15° -1 ]

Sqrt of [ 3.04 + 1.07 -1] = 1.765 or ~ 55-56°

How did you work yours out?

[rexford]

For those who have accused me of blatant German bias in the past, my dresser is the proud home of TEN (10) Matchbox 1/76 scale Fireflies. Was going to cut down the barrels on most of them to make 75mm L40 Shermans, but that would be sacrilegious.

Matchbox Fireflies are not only good against Matchbox Panthers when APDS is flying right, but 17 pounder can pound the tar out of Matchbox JagdPanzer IV with 80mm armor. Matchbox 1/76 scale is cheap and easy to obtain, compared to fujimi which almost costs three times as much.

And Matchbox 17 pounder APCBC doesn't self-destruct after it penetrates spaced armor on M.B. PzKpfw III, cause it is solid shot.

By numbering my Fireflies, German players don't know which is the real 17 pounder and which is a 75mm "door knocker".

So there!

[Claus B]

Originally posted by rexford:

Computed the gun elevation angles for 17 pounder APCBC and APDS against targets at 500, 800, 1100 and 1400 meters. In all four cases, APDS gun elevation angle is about 55% of APCBC.

If this ratio was known by authorities (good likelihood), and was given to Firefly crews (good chance), crews in field might be able to correct for absence of APDS lines by roughly "halving" APCBC elevation.

This subject does require more info on exactly what was done to properly aim APDS.

You are actually spot on. In a 1952 training manual for the SP 17-pr M10 you find the following:

---------

Order: "Sabot"

The gunner will set false range on the APCBC scale, ie, he will set half the range ordered.

---------

The sight in question is the Telescope No43 x 3 ML Mk 3, the round is Cartridge QF 17-pr AP/T/DS Mk 2. It seems similar to the WWII round and the projectile data are the same for the Mk IB and MkII. Based on data from Hunnicutt (who does not give the mark of round) these projectiles are are 2 ounces heavier at 7.11 than the round described by Hunnicutt (at 7.9). Muzzle velocity are the same at 3,950 fps and the operation of the rounds look similar.

The training manual states that the AP/T/DS Mk II has been declared obsolete and are to be replaced by a pot-type sabot. This is in 1952.

Claus B

[rexford]

Thanks for valuable info on actual procedure used to fire APDS using APCBC range scale.

Did an analysis of what it means to use half of the APCBC setting when it should be 0.555, a 10% error. Sounds small and insignificant, but......

APDS MPI (MEAN POINT OF IMPACT) error due to "make believe" range scale (take half of APCBC):

500m

10% angle error throws mean trajectory off aim point by 0.1m

800m

10% angle error results in 0.3m error

1100m

10% angle error puts mean point of impact 0.5m away from aim point

1400m

10% angle error is associated with 0.8m error

Now this is the impact if the range was perfectly known to the target, which it isn't. There is also shot scatter based on other random factors.

If APCBC results in a hit at 1500m on the Tiger II turret center, for instance, and the gunner then switches to APDS to kill the beast, first shot aim will be off by about 1m vertical. This is enough to greatly increase the percentage of APDS shots that miss the target on the first shot.

Since APDS isn't too abundant and about half the shots have that nasty habit of missing anything and everything due to sabot problems, and won't pierce even if they hit, first shots at 1500m will be a waste of ammo alot of the time.

I wonder if scenario's like this resulted in orders to only use APDS at short and medium ranges during WW II. Even after the war with better APDS and solutions to other APDS problems, trying to get by using half the reading on APCBC scale greatly reduces first shot accuracy with expensive ammo.

Regarding German accuracy relative to British, British documents state that using APDS reduces accuracy of following attempts with APCBC, something that does not happen with HVAP. And British gun sights could go out of alignment due to recoil, and they wonder if German sights are similar. And there are notes that German sights are superior to American/British cause they are more accurate and work better in dim light/overcast conditions/days without bright sunshine. And so on and so on.

Given equal range estimation and round to round scatter, all of this suggests that Tiger hit probability could be higher than 17 pounder APCBC at range due to better sights, and no APDS that messes up sights.

Better sights give Germans an advantage in terms of hit % on first shot and follow-up. Sorry to say this in terms of Firefly survival, but it seems to be true.

We can theoretically calculate hit % based on trajectory and dispersion and range estimation error, but it is all garbage if gunsight limitations and problems are not cranked into the equation. Another advantage to panzers.

[rexford]

Here' some stuff on 17 pounder APCBC and APDS against angled targets at 500m and 1000m:

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

80mm Panther glacis plate at 55 degrees, 0.93 quality due to flaws (this is quality when 76.2mm hits 80mm plate at 55 degrees for medium severity flaws or brittleness)

APCBC can't penetrate

APDS penetrates at 1700m

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

85mm Panther glacis plate at 55 degrees, 0.93 quality due to flaws

APCBC is no good

APDS penetrates at 1300m

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

80mm Panther glacis plate at 55 degrees,

1.00 quality due to absence of flaws (which occurs about half the time, maybe)

APCBC bounces all the time

APDS penetrates at 1300m

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

85mm Panther glacis at 55 degrees, 1.00 quality

APCBC is useless

APDS penetrates at 1000m

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

APDS fails to penetrate Panther glacis at Isigny due to the sabot problems, which is clear when one looks at the trouble they had hitting what they were aiming at. My analysis of what happens when half of APCBC range scale is used for 17 Pdr APDS shows that absence of range lines for APDS should not throw off Isigny shots by enough to explain the bad showing. The ranges vary from 200 yards to 800 yards.

APDS at Isigny was striking Panther glacis with enough yaw angle to destroy penetration even if it could hit, it would seem.

Many Russian, American and British sources list Panther glacis at 85mm thickness, and Panther nose at 60mm to 75mm. Actual measurements on nose armor show that it exceeded the usual assumed thickness of 60mm by over 10% (see Isigny firing test report). As war carried on, quality control may have allowed over-thickness plates for one reason or another to speed production, reduce number of plates disallowed for too much thickness, etc.

85mm Panther glacis explains alot of firing test and battlefield reports. Plate is 6.3% thicker than 80mm, and slope effect will be larger, and quality will be larger even with flaws (due to T/D ratio), so 85mm glacis is alot more resistant than 80mm.

[rexford]

To cover all the bases, did American sights have specific range lines for 76mm and 90mm HVAP?

Is it safe to assume that U.S. 57mm ATG didn't have sights for APDS? This might account for some of the inaccuracy noted in firing tests against Panther with 57mm M1 gun.

Using APCBC range lines for APDS shots against moving targets could also result in misses if gunner forgets to take percentage of APCBC lead. Too much lead for speedy APDS.

Looks like Conall's post has opened up a new and valuable "can of worms".

And, of course, how many Stuarts and 2 pounder equipped AFV had range sights graduated for Littlejohn adaptor?

Tungsten is great if sights include it.

[:USERNAME:]

Originally posted by 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

.

I would like to see your references.

By the way, you confuse trajectory and yaw in another post. Tarjectory has to do with the translational motion of a projectile; I.e., its path. Yaw has to do with the rotational motion of a projectile about an axis.

Pitch deals with the projectiles nose going up or down. Yaw deals with rotation that would make the nose go left to right (like slip in a airplane). Roll has to do with the round spinning about its centerline.

http://www.missing-lynx.com/gallery/canada/emhybrid.htm

Heres a website showing a model of a firefly using some sort of barrel weight. It shows the barrel being painted white in an effort to camoflauge itself. What the bulge in the middle of the barrel is something of a mystery.

I still can provide data on the US and British sharing of APDS during the war.

[Paul Lakowski]

Originally posted by Claus B:

You are actually spot on. In a 1952 training manual for the SP 17-pr M10 you find the following:

---------

Order: "Sabot"

The gunner will set false range on the APCBC scale, ie, he will set half the range ordered.

---------

It seems similar to the WWII round and the projectile data are the same for the Mk IB and MkII. Based on data from Hunnicutt (who does not give the mark of round) these projectiles are are 2 ounces heavier at 7.11 than the round described by Hunnicutt (at 7.9). Muzzle velocity are the same at 3,950 fps and the operation of the rounds look similar.

Claus B

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?

[Conall]

References:

Re the sights:

A Guide to A.F.V. Telescopes, A.F.V. publications section, A.F.V. School Bovington, War Office AFVP/MSC/64 March 1945

This covers all the British & US sights in use at that time & includes some obsolete sights as well. The document runs to 64 pages & includes schematics & specifications plus some additional notes. The detail specific to the 17pdr is on pages 26 to 33, the 6pdr sights are covered on pages 12 to 19, & the 77mm on pages 34 to 37. Although all these guns were issued SVDS (APDS) ammunition at various times in 1944-45, none of the sights issued had any graticules for this ammunition. This is in stark contrast to APC, APCBC, HE & MG, all of which have range scales marked on the sights.

Regarding the problem of muzzle brakes, see:

Military Ballistics, ed. G.M. Moss, D.W. Leeming, & C.L. Farrar, RMCS, Brassey's 1983, ISBN 1 85753 084 5. Specifically see chapter 3 "Intermediate Ballistics" page 64-65

An efficient muzzle brake can reduce recoil by over 50%, though such muzzle brakes are complex, costly and, as has been indicated, can damage hearing. Practical muzzle brakes reduce recoil by about 25% by deflecting some of the gas flow sideways rather than backwards. Muzzle brakes can be designed to deflect gas mainly upwards, for example to control upward muzzle jump. The prime disadvantage of the muzzle brake is that it increases the blast noise suffered by the firer. It can also subject the fore-end of the barrel to excessive stress. Generally sabotted ammunition cannot be used in guns fitted with muzzle brakes as the complex gas flow at the muzzle interferes with the sabot discarding process, thereby reducing the accuracy of fire. Besides the sabot is very likely to collide with the muzzle brake.

The Bovington Fire & Movement pamphlet, 1975 shows schematics of two types of SABOT - the pot type that had a single SABOT, which discarded as a whole axially & the petal SABOT, which discarded radially into several pieces - the latter as Claus has indicated was the more successful post-war design.

For the best explanation of the process see:

R.M. Ogorkiewicz, Design & Development of Fighting Vehicles, MacDonald & Co 1968, ISBN 356 01461 4, pp 58 & 60-63. He notes that the problems with APDS ammunition (disturbances arising during separation etc) were principally solved in the late 50's & early 60's by the Britsh & Canadians working at the Canadian Armament Research & Development Establishment, at Valcartier, Quebec.

The problem for the British was that in 1944 SVDS (APDS) was an experimental technology, wheras APCBC was a proven type of ammunition. The priority was therefore, for the 17pdr to operate best (most accurately with the most efficient recoil forces) with APCBC ammunition. The muzzle brake was therefore, essential to reduce recoil to an acceptable limit, given the restrictions on how difficult it had been to shoe the 17pdr & it's trunnions into a Sherman turret (see David Fletcher, The Universal Tank, London HMSO 1993, ISBN 0 11 290534 X, pp. 81-85). The imperative need was limiting the recoil forces & the subsequent gun jump, a process which required a muzzle brake. See also WO 291/1263 Firing trials with 17pdr in Sherman I using APC & discarding sabot shot, 1944 & WO 291/324 Accuracy of first round of an anti-tank engagement of a stationary target using APCBC & APSV/DS ammunition, 1946. It's also worth noting that most 6pdr guns, mounted on the Churchill MkIII & MkIV either had no muzzle brake or had the muzzle brake removed once the SVDS (APDS) ammo was available. Likewise the 20pdr had no muzzle brake (see WO 342/1 Tanks Battle Performance & Tactics 1951-53 1953 for a discussion of the relative merits of 20pdr APCBC & APDS ammunition)

The muzzle weight issue is a complete red herring - on the Achilles it was mounted primarily to balance the gun, as unlike the Sherman the turret was not sufficiently heavy to do so - there was also a counterweight on the back of the turret. The object which appears on the middle of some 17pdr gun barrels is nothing more than a fake muzzle brake, placed in an attempt to camouflage the long 17pdr barrel & make it appear more like a L/40 75mm barrel. For more on this see http://www.activevr.com/afv/muzzle.html#dragon & http://www.activevr.com/afv/camouflage/shrmic.html & http://www.activevr.com/afv/camouflage/shrvc1.html

I look forward to seeing other sources on the subject. The one's I have quoted are by no means exhaustive, but they do represent a reasonable survey of the subject. For more on the Firefly specifically I would suggest

David Fletcher: Sherman VC M4A4 Firefly, Militayr Ordnance Special Number 19, Darlington Productions 1997.

regards,

Conall

[This message has been edited by Conall (edited 03-11-2001).]

[Conall]

Originally posted by :USERNAME::

I would like to see your references.

See above ad nauseam.

http://www.missing-lynx.com/gallery/canada/emhybrid.htm

Heres a website showing a model of a firefly using some sort of barrel weight.

Nope that's a rather badly modelled fake muzzel brake.

I still can provide data on the US and British sharing of APDS during the war.

I look forward to seeing them, but I'm not holding my breath.

Conall

[rexford]

Thanks Conall for authoritative and well documented analysis of 17 pounder problems firing APDS. It looks like it would be natural for a high percentage of APDS shots to have reduced accuracy and penetration, due to 17 pdr muzzle brake and sabot shed problems.

Our booklet will analyze the percentage of 17 pounder APDS shots that perform as if problems did not exist.

CM should do something about APDS from 17 pounder if game is to be realistic, which includes decreasing the slope effect when the ammo is working correctly (however often that may be).

[rexford]

Robert Livingston advised me that U.S. gunners were given cards for HVAP use that identified range scale settings to be used, and they seem to have worked well since 76mm HVAP was one of the most accurate projectiles of WW II, if not the most accurate.

90mm HVAP users also seemed quite happy with accuracy.

We have a British report where 76mm HVAP is noted as having the smallest scatter about aim point of any WW II ammo, even better than 76mm APCBC which had been the best. And 76mm HVAP did not throw off accuracy of later shots with APCBC.

Inconsistent APDS performance from Firefly was probably accepted as the price to pay for superior APCBC performance against Tiger front and Panther mantlet. Good points Conall.

[:USERNAME:]

Originally posted by Conall:

I look forward to seeing them, but I'm not holding my breath.

Conall

Hey are you the Conall from Panzer Elite? I almost forgot how much I dislike your posting style.

Heres a better website bub.

http://web.inter.nl.net/users/spoelstra/g104/firefly.htm#ffcamouflage

I think you may need to catch up old boy. Start from the beggining of the thread and read all the words real closely. I mentioned that the achilles had some sort of weight on its barrel and this serendipitously would stop muzzle jump. How thats a red herring is beyond me. The basic physical fact is that mass resists movement. Called Inertia by alot of english speaking people. So muzzle brakes have inertia and so did that weight at the end of the achilles.

So your source claims that APDS cant be fired from a muzzle braked weapon? Thats interesting. You got wrecksford all excited about that? Aside from the fact that the 17lbr is braked and fired APDS, do you see anything wrong with that picture? The sabots need some interaction with the atmosphere to discard. That doesnt happen till the shell is a little clear of the end of the barrel. XRay photos backed it up. It was known in 1945.

Ill have to go to my car and get my notes. In the meantime. Please use good sources like myself.

lewis

[Paul Lakowski]

Originally posted by :USERNAME::

Hey are you the Conall from Panzer Elite? I almost forgot how much I dislike your posting style.

Heres a better website bub.

http://web.inter.nl.net/users/spoelstra/g104/firefly.htm#ffcamouflage

I think you may need to catch up old boy. Start from the beggining of the thread and read all the words real closely.

....and Lewis you have an abrasive approach, which makes discussing things with you very difficult at times. If the aim is to share info , why don't you control your sarcastic tone and just stick to the facts. Its hard enough as it is with out having to deal with all that crap.

[Claus B]

Originally posted by rexford:

Did an analysis of what it means to use half of the APCBC setting when it should be 0.555, a 10% error. Sounds small and insignificant, but......

APDS MPI (MEAN POINT OF IMPACT) error due to "make believe" range scale (take half of APCBC):

500m

10% angle error throws mean trajectory off aim point by 0.1m

800m

10% angle error results in 0.3m error

1100m

10% angle error puts mean point of impact 0.5m away from aim point

1400m

10% angle error is associated with 0.8m error

Now this is the impact if the range was perfectly known to the target, which it isn't. There is also shot scatter based on other random factors.

If APCBC results in a hit at 1500m on the Tiger II turret center, for instance, and the gunner then switches to APDS to kill the beast, first shot aim will be off by about 1m vertical. This is enough to greatly increase the percentage of APDS shots that miss the target on the first shot.

Remember that, as per the manual, 17pdr APDS was not to be used at ranges above 1000 yards (extreme engagement range).

Claus B

[Claus B]

Originally posted by :USERNAME::

I mentioned that the achilles had some sort of weight on its barrel and this serendipitously would stop muzzle jump. How thats a red herring is beyond me. The basic physical fact is that mass resists movement. Called Inertia by alot of english speaking people. So muzzle brakes have inertia and so did that weight at the end of the achilles.

It is not so much whether the counterweight on the SP 17pdr M10 had effects on muzzle jump or not. It was not put there with this in mind. The 17pdr AT-gun in its most common form (on the Mk 1 carriage) had no such counterweight, nor did the Firefly (except as a decoy). If the counterweight was used as means to eliminate barrel jump when firing APDS, then I would expect it to be found on all 17pdr guns.

Another interesting thing about 17pdr muzzle weights are that they were round on some early 17pdr AT guns on the Mk 2 (25pdr)carriage long before the issue of APDS. In this case, it seems to be an attempt to balance the gun in a carriage it was not designed for. Any takes on this one?

Originally posted by Conall:

The muzzle weight issue is a complete red herring - on the Achilles it was mounted primarily to balance the gun, as unlike the Sherman the turret was not sufficiently heavy to do so - there was also a counterweight on the back of the turret.

This I do not understand. Who could the turret balance the gun?

Claus B

[Conall]

Originally posted by :USERNAME::

Heres a better website bub.

http://web.inter.nl.net/users/spoelstra/g104/firefly.htm#ffcamouflage

Agreed it is a better website, & it shows that the object in the middle of the barrel of the Firefly mounted 17pdr was a fake muzzle barrel.

So your source claims that APDS cant be fired from a muzzle braked weapon? Thats interesting. Aside from the fact that the 17lbr is braked and fired APDS, do you see anything wrong with that picture?

No, the source I quoted didn't say that sabotted ammunition couldn't be fired from guns with muzzle brakes. It said that doing so would very likely cause a uneven discard & therefore create an unacceptable degree of round instability. It also pointed out that there was a risk of the muzzle brake being damaged. So one more time, just for you, the British had designed the 17pdr to fire AP, APC, & APCBC, for which the muzzle brake was essential in reducing recoil forces to an acceptable level. Having done so they then developed SVDS, and accepted the pay off of a more inaccurate round & much higher barrel wear because they needed the improved penetration. A simple aspect of wartime expediency & having to make trade-offs. Once the war was over however, they had the luxury of producing new guns specifically designed to fire APDS ammunition (20pdr etc). Note the rather glaring absence of a muzzle brake on the 20pdr.

The sabots need some interaction with the atmosphere to discard. That doesn't happen till the shell is a little clear of the end of the barrel.

No ****, Sherlock! However, I think you should brush up on your intermediate ballistics. Not only does the shell clear the end of the barrel, so does the precursor blast shock (gases preceding the projectile down the barrel). These are followed by the blast shock & the projectile - the propellant gases rapidly expand, accelerating to velocities much greater than that of the projectile. Even under ideal circumstances the action of the muzzle gas flow can have an adverse effect on the accuracy of the gun by causing abnormal yawing of the projectile. This whole process is made much more complex by the effect of the muzzle brake & in particular exacerbates the effect of the muzzle gas on the sabotted ammo as it discards.

I look forward to seeing the finding from your notes.

Conall

[Conall]

Originally posted by Claus B:

This I do not understand. Who could the turret balance the gun?

Claus B

Claus, my bad for a) expressing myself unclearly & talking about two vehicles at once. As I understood it the M10 series required a weight at the back of the turret to balance the weight of the 3" gun (see Hunnicut, Sherman p.366). The Sherman series (either the 75mm or 76mm) didn't need this as the gun was sufficiently balanced in the turret (not least because the turret was much heavier than the open topped M10). In the case of the Achilles the 17pdr was a lighter gun, which didn't require the rear turret counterweight to such an extent, so rather than remove it, it was easier to fit another counterweight on the barrel. Apologies for creating any confusion - your article explains it rather better. http://www.panser.dk/profiler/achilles/achilles.htm

Finally in the case of the Sherman Firefly, the radio in the ad-hoc rear extension to the turret acted to counter-balance the weight of the 17pdr. 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.

Regards,

Conall

[This message has been edited by Conall (edited 03-11-2001).]

[rexford]

Claus B.

Thanks for noting 1000 yard limit on APDS use, somehow I didn't notice this. This range limitation was in 6 and 17 pdr manuals for APDS during WW II?

When British test fired 6 pounder APDS against a captured Tiger during 1945, they had no problem saying round would penetrate beyond 1000 yards. The fact that they tested APDS with impact velocities expected beyond 1000 yards suggested that APDS could be used at any range.

We thought the use of 1000+ yard velocities in penetration tests meant that APDS could be used beyond that range.

[Claus B]

Originally posted by rexford:

Thanks for noting 1000 yard limit on APDS use, somehow I didn't notice this. This range limitation was in 6 and 17 pdr manuals for APDS during WW II?

I dont know about the 6pdr.

The "Extreme range (effective) for the 17pdr is given as 1000 yards in "Royal Armoured Corps Training, Vol. III - Armament, Pamphlet No. 7, SP 17-pr M10, 1952". As previously stated, the ammo looks for all intents and purposes to be similar to the WWII round.

The same 1000 yards limitation is found in Fletchers book on the Firefly mentioned by Conall: "Unfortunately APDS...proved to be wildly inacurrate at anything over 1000 yards."

Originally posted by rexford:

When British test fired 6 pounder APDS against a captured Tiger during 1945, they had no problem saying round would penetrate beyond 1000 yards. The fact that they tested APDS with impact velocities expected beyond 1000 yards suggested that APDS could be used at any range.

If these are the tests found in Jentz: "Tiger I & II - Kampf und Taktik" (the english title eludes me at the moment), then you are correct that they concluded that 6pdr APDS and 17pdr APDS could penetrate various bits and pieces of the Tiger at impact velocities corresponding to ranges beyond 1000 yards.

However, these tests were conducted at a range of 150 feet using different propelling charges to simulate different impact velocities corresponding with different ranges.

At 150 feet, accuracy is not likely to have been an issue.

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.

So, while the 17pdr APDS could certainly do damage above 1000 yards, that would be of little use if the shot would never hit the target.

Claus B