Home Forums WWII Anti-tank rifle armour penetration figures

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  • #138334
    John D Salt
    Participant

    Having recently purchased Steve Zaloga’s Osprey on anti-tank rifles, I tapped the penetration data into a spreadsheet to find out how believable the numbers were. This is a more comprehensive set of penetration data for this class of weapon than I have ever seen anywhere else, so I include a listing of some key snippets, including penetration at normal impact at 100 and 300 metres.

    How well, I wondered, do the penetration figures given match those produced by my favourite armour penetration formula? (TL;DR — pretty darn well, except for the Short Solothurn).

    It is unfortunate that even such an illustrious commentator as Zaloga doesn’t give the source of the numbers or say how they were obtained, nor give any information on the target plate or penetration criterion used. Still, never mind, almost nobody does, I ought to be used to it by now.

    Since it is easy enough to work it out, I do not include here the figure for kinetic energy; I note, however, that some of Zaloga’s KE figures do not quite match those my spreadsheet produced using the projectile masses and velocities given.

    My first step was to extrapolate from the figures given what penetration would be at the muzzle, using the GROWTH() spreadsheet function. The result I compared with the penetration figure produced by my favourite armour penetration formula, the one published by James Dehn in 1986, using the projectile mass and muzzle velocity.

    Because the lightly-armoured vehicles anti-tank rifles were effective against tended to use homo-hard armour, I chose a target plate with ultimate tensile strength (UTS) of 1000 MPa. As a rule of hand-waving generality, armour plate reduces in strength as it gets thicker. According to another spreadsheet I have lying around which I may bore you with some day, that would be about right for an average (from the mulch of snippetry in the spreadsheet) rolled plate of about 30mm thickness.

    With all these assumptions and limitations in mind, it is not vastly discouraging to discover that the average of the Dehn-calculated figure lies within 1% of the average of the figures given in the table. The worst matches are about 30% under and over the table figure.

    An additional complication to be considered is that most of the projectiles in question were jacketed rounds, so it would doubtless be better to consider the mass and dimensions of the penetrating core, rather than the whole projectile. The 20mm rounds seem to have been solid chunks of steel. I expect this makes the biggest difference in the case of the two projectiles that have tungsten-carbide (TC) cores, the Patrone 318 and BS-41. Since these and a couple of other weapons have muzzle velocities a little over 1000 m/s, they are on the limit of applicability of Dehn’s formula. Arguably the Lanz-Odermatt formula might give a better estimate of penetration, but it would require yet more information about core dimensions that is not given. You never get the data you want, only something in the neighbourhood, maybe two doors down.

    Doing a bit more flonking around the interwebs, I managed to find in odd drawings and postings from cartridge nerds the following data about the penetrating cores of some of the projectiles:

    TuF core diameter 10.29mm
    Boys W Mk 1 core mass 37.0g
    Boys W Mk 2 core mass 28.9g
    PzB 39 core mass 8.7g core diameter 6.13mm
    BS-32 core mass 63.4g
    BS-41 core mass 38.2g core diameter 10mm

    Having discovered the length of the TuF bullet to be 51.56mm, and the head shape to be a 4.6 calibre radius head tangent ogive, I dusted off an old Python script to calculate the mass of tangent ogive projectiles of known dimensions and density. This gives an estimate of 27.2g for the core mass. This is certainly an over-estimate, as the Python script works for square-tailed bullets, and the TuF core has a boat tail.

    As I had no dimensions for the Boys cores, I simply twiddled the core diameter until the Dehn function produced the same number given in Zaloga’s table. This is, of course, cheating, but if it turns out that the core diameter is 13.2mm for the W Mk I and 11.7mm for the W Mk II, then Dehn will have been amply justified.

    Using the core masses and diameters found for the other rounds improves the match between the Dehn formula results and those given in the table to a remarkable extent. Results for the T-Gewehr, 14.5mm B-32, Type 100 and both Long Solothurn guns are within one millimetre after rounding; those for the tungsten carbide-cored weapons are off by 3 or 4 mm.

    The Polish KbP wz.35 (Maroszek) is a bit of an odd fish, as it uses a soft lead core, with the intention of producing behind-armour damage by means of the Hopkinson effect (spalling) rather than punching a hole in the armour. As no data on core dimension could be found, it is perhaps not surprising that the result from Dehn’s formula is off by 4mm.

    The worst mismatch is for the S 18-100 Short Solothurn, out by a whole 9mm, or more than 25%. Given the absence of any known design strangeness in the round, and the excellent match found for all the Long Solothurn rounds, this is a mystery, which I cheerfully attribute to a cockup of some kind in the figures. Otherwise, the pretty good match to Dehn’s formula leads me to believe that Zaloga’s numbers are reasonably trustworthy for all the other cases.

    I did not bother to repeat the exercise for the penetration figures given at 30 degrees, but a comparison between them and the normal impact figures indicates that weapons in this class lose performance with angled impact to a greater extent than bigger weapons. My favourite WW2 OR general-purpose basis curve has it that a 30-degree (British; 60° NATO) impact should reduce the expected penetration to 80% of that at normal. For these weapons, the figure varies between 56% and 80%, with an average of 68%.

    					
    Weapon		Cartridge	Designation	V0(m/s) Core	Proj 	 Pen(mm) at	
    								mass(g) 100m	300m
    T-Gewehr	13.2×92SR	TuF		  780	steel	 51.5	 20	 15
    KbP wz.35	7.92×107	DS		1,280	lead	 14.6	 33	 16
    PzB 39		7.92×94		Patrone 318	1,160	TC	 14.8	 30	 23
    Boys		13.9×99B	W Mk I		  750	steel	 60.2	 17	 14
    Boys		13.9×99B	W Mk II		  885	steel	 47.6	 23	 21
    PTRS/PTRD	14.5×114	B-32		1,012	steel	 64.2	 40	 35
    PTRS/PTRD	14.5×114	BS-41		1,012	TC	 64.4	 50	 40
    S 18-100	20×105B		Short Solothurn	  750	steel	140.0	 35	 27
    S 18-1000	20×138B		Long Solothurn	  910	steel	147.0	 40	 35
    Lahti L-39	20×138B		Long Solothurn	  840	steel	147.0	 37	 33
    Type 97		20×125		Type 100	  805	steel	156.0	 35	 30
    

    There’s a lot more in Zaloga’s book than just the penetration figures, so I recommend it to everyone.

    It is obvious from the book that, as well as impuissant penetration performance, all weapons in this class suffered from a lack of behind-armour effect, but I have yet to discover any satisfactory simple method of assessing that.

    All the best,

    John.

    #138337
    Whirlwind
    Participant

    Thanks John, that is amazingly useful.  And explains entirely the difference between what I have been reading lately in British accounts (ATRs were literally useless from February 1941 onwards) and what Ivan has been looking at regarding massed Soviet ATR attacks against the flanks of Panther tanks.

    https://hereticalgaming.blogspot.co.uk/

    #138347
    Patrice
    Participant

    Very interesting, thanks.

    http://www.argad-bzh.fr/argad/en.html
    https://www.anargader.net/

    #138356
    MartinR
    Participant

    Fascinating stuff, I amazed at how lousy the Boys was and how good the PTRS  is. No wonder the Russians kept them.

    The ATR penetration data I’ve seen before has generally been madenningly vague.

    "Mistakes in the initial deployment cannot be rectified" - Helmuth von Moltke

    #138365
    deephorse
    Participant

    This data backs up comments I’ve read from B.E.F. soldiers that the Boys was useless.  It was also illustrated in a recent documentary on Dunkirk (I think it was) where there was a modern day test firing of a Boys against a vertical 30mm plate (again, I think it was!).  The range to the plate wasn’t given, but the round just bounced off.

    #138366
    Norm S
    Participant

    Thanks John.

    #138372
    John D Salt
    Participant

    There seem to have been three ways people thought of to improve the performance of the original T-Gewehr.

    1. Jack up the velocity.

    2. Whomp up the calibre.

    3. Use something other than steel in the penetrating core.

    Different nations plumped for different choices.

    The Poles went for 1 and 3, with the odd choice of lead as the core material, and the use of a highly efficient muzzle brake making a nice light weapon.

    The Germans went for 1 and 3, with a more conventional choice of tungsten carbide for the penetrating core, but with a bit of a pointless and legally dodgy diversion into adding a tear-gas carrying pellet to increase behind-armour effect, which it didn’t.

    Having first experimented with the deliciously strange Kurchevsky 37mm recoilless anti-tank rifle, the Soviets chose 1. They did not reduce the calibre of the bullet to that of an ordinary rifle, accepting the consequent heftiness of the weapon. Later they added 3 as well. They were also the only nation to emphasise the tactical use of such weapons en masse, instead of distributing one to each platoon or so.

    The Swiss, Finns, and Japanese all decided on 2, going to 20mm calibre and producing some prodigiously cumbersome weapons for their poor soldiers to lug about.

    The Czechs’ ATR developments were rudely interrupted by the Germans, and so ended up being quite like the Germans’, but with the novelty of the first service weapon to have a bullpup layout.

    The Italians, Rumanians and Hungarians all seem to have been content to use other people’s ATRs, either bought from the Swiss or nicked from the Poles.

    The French and Americans both sensibly decided that this was a class of weapon not worth pursuing.

    The British alone seem to have considered it worth developing a weapon of much the same calibre, muzzle velocity, and overall weight as the original T-Gewehr, whose penetrating performance it exceeded only with the introduction of the Mk II bullet. The belated decision to try methods 1 and 3 from the list above produced a prototype that would have become the Mk III bullet had it been accepted for service, but by that time the PIAT was clearly the way forward.

    All the best,

    John.

    #138400
    Ivan Sorensen
    Participant

    This is fantastically useful and as people mention upthread, definitely helps account for very different perceptions.

    The British seem to have been rather dismayed by theirs and as far as I know most of the German rifles ended up being converted to grenade launchers.
    Meanwhile while the odds of flat out stopping a tank remains low, the Soviets getting a potential 40mm of penetration is not something to be dismissed for sure.

    Nordic Weasel Games
    https://www.wargamevault.com/browse/pub/5701/Nordic-Weasel-Games?src=browse5701

    #138413
    John D Salt
    Participant

    I was wondering if I was being too harsh on the Boys; some British weapons have had relatively ungenerous performance estimates compared to the optimistic “Manufacturer’s brochure” figures quoted by other nations. Possibly the British used stronger plate in their proof tests?

    Having given the matter a few minutes’ thought over a glass of tea, I really don’t think that’s the case.

    In the first place, if the British are not usually given to wild over-claims for weapon performance, still less so are the Russians. Russian official penetration figures are famously conservative, to the extent that MI 10 also gave, alongside the official figures, estimates of penetration based on British practice that were always more generous.

    In the second place, as severe armour nerds might recall from a 2015 posting of mine on proof conditions for British A/Tk guns, the plate used from 1936 to 1942 had an ultimate tensile strength between 70 and 75 tons. I assume that the same plate was used for anti-tank rifles as for anti-tank guns. Further assuming that this means tons per square inch — hard to see what else it could be unless the proof plate has the strength of plasticene — this is a range of 965 to 1034 MPa, with 1000 MPa slap bang dab in the middle. Lucky guess by me, and as shown it is a good match for almost all the ATR steel projectiles of known dimensions.

    It seems that the Boys did have its afficionados — Boys fan-boys, I suppose — but only really among strange special forces types. The LRDG thought it was a fun gun to shoot up aircraft on the ground, and the US Marine Raiders used it in the Pacific to shoot up, among other things, enemy boats. Those are obviously not tanks; this really corresponds to the post-war idea of an anti-material rifle. Otherwise the attitude of the Army seems well reflected in a remark reported by Zaloga from the Desert war, that the Boys was usually “given to the company drunk to carry as penance”.

    All the best,

    John.

    #138435
    deephorse
    Participant

    A bit like choosing who got to carry the ’84’ on exercise then?

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