Requesting data on the German 50mm Kw.K.38 L/42

[Oudy]

I need a little assistance from ballistics experts.

I'm trying to add a Pz.IIIG with a 50mm Kw.K.38 L/42 (short 50mm gun) to the game. The Pz. III with the short 50mm gun is not in the game, but it was a major player in Barbarossa. It is simple to switch guns and alter armor values, but the data for the this gun isn't in the game data files.

I have the penetration data from Jentz, but I need some additional information.

Info needed:

Reload time or Rounds per minute

Maximum firing distance

Muzzle velocity for the 50mm SPgGr 38 (HE) shell

It would also be nice to have additional penetration data (other than Jentz)

Finally, does anyone have the mathematical formula for converting armor penetration values from 30 degrees to 0 degrees?

Thanks in advance for any assistance.

Oudy

[FinnN]

I guess it'll be (penetration at 30 degrees) x (Cosine 30 degrees), so 0.866xP.

Have fun

Finn

[Kharnvor]

I would surmise, since it's the exact same shell, just fired out of a shorter barrel, the reload time would be the same.

[Oudy]

Kharnvor

I assumed that as well, but when I looked at the reload rate for different 75mm guns they were different, so I just wanted to verify for accuracy.

Oudy

[Jeff Duquette]

Originally posted by FinnN:

I guess it'll be (penetration at 30 degrees) x (Cosine 30 degrees), so 0.866xP.

Have fun

Finn

Of course penetration should be greater at 0-degrees than 30-degrees -- not less as you have implied with the above. I think what you are trying to say is given penetration at 30-degree obliquity what is penetration at 0-degrees. Assuming a simple cosine function for slope effect the answer is:

Penetration @ 30-deg divided by COS(30) = Penetration @ 0-degrees.

But this particular type of AP projectile is not well suited to prediction of penetration via a simple cosine function -- that is it's not well suited for any sort of plate inclination beyond about 8 or 10-degrees from the normal. Moreover, the actual performance vs. a cosine function diverges rapidly beyond about 8 or 10-degrees.

[Jeff Duquette]

Originally posted by Oudy:

I need a little assistance from ballistics experts.

I'm trying to add a Pz.IIIG with a 50mm Kw.K.38 L/42 (short 50mm gun) to the game. The Pz. III with the short 50mm gun is not in the game, but it was a major player in Barbarossa. It is simple to switch guns and alter armor values, but the data for the this gun isn't in the game data files.

I have the penetration data from Jentz, but I need some additional information.

Info needed:

Reload time or Rounds per minute

Maximum firing distance

Muzzle velocity for the 50mm SPgGr 38 (HE) shell

It would also be nice to have additional penetration data (other than Jentz)

Finally, does anyone have the mathematical formula for converting armor penetration values from 30 degrees to 0 degrees?

Thanks in advance for any assistance.

Oudy

Oudy:

Excellent idea. The game does need the earlier PzIII models.

Regarding your slope effects question, it is complicated as slope effects are a function of obliquity, t/d ratio and projectile type. German wartime estimations also included a slope effects factor related to impact velocity.

I have not looked at this two carefully in game terms, but as I understand this from earlier disscussions on the subject, the Anglo-Allied penetration figures represent 0-degree values. What you might initially try looking at is obtaining 30-degree penetration values for Allied guns firing the same form of projectile as your 50mmL42 KwK. I think the early 50mm KwK would be firing mostly APC, so look for Allied guns in this caliber range and same projectile type -- 2pdr, 6pdr, 75mm are possible candidates. Divide the 0-degree values provided in the game by the 30-degree values you have obtained from a little bookshelf research. This will give you an idea of what sort of slope effects multiplier the game designers may be employing.

Moreover, lets say the game data for a specific gun has a penetration value of 50mm at 100-yards at 0-degrees. Pop open one of your tank books (or do a google) to see what the author gives for 30-deg penetration. Most references indicate penetration in terms of 30-degree obliquity. Lets say the reference indicates the gun does 40mm at 100-yards at 30-degrees. Your slope effect is than the game 0-deg penetration value divded by the 30-deg value....50mm/40mm = 1.25. In other the game designers are implying that the projectile type does 1.25 times more penetration at 0-degrees than it does at 30-degrees.

[ June 06, 2007, 01:49 PM: Message edited by: Jeff Duquette ]

[FinnN]

Originally posted by Jeff Duquette:

</font><blockquote>quote:</font><hr />Originally posted by FinnN:

I guess it'll be (penetration at 30 degrees) x (Cosine 30 degrees), so 0.866xP.

Have fun

Finn

Of course penetration should be greater at 0-degrees than 30-degrees -- not less as you have implied with the above. I think what you are trying to say is given penetration at 30-degree obliquity what is penetration at 0-degrees. Assuming a simple cosine function for slope effect the answer is:

Penetration @ 30-deg divided by COS(30) = Penetration @ 0-degrees.

But this particular type of AP projectile is not well suited to prediction of penetration via a simple cosine function -- that is it's not well suited for any sort of plate inclination beyond about 8 or 10-degrees from the normal. Moreover, the actual performance vs. a cosine function diverges rapidly beyond about 8 or 10-degrees. </font>

[SlapHappy]

Oudy

This website has lots of credible-looking info about WWII tanks, small arms, etc. for many nations and is beautifully organized.

http://www.tarrif.net/

[Jeff Duquette]

Never mind about my last idea. I started looking at the games slope effects model, and I’m not quite sure what to make of it yet. Below are comparisons of actual terminal effects data for the US Army’s 57mm M1 antitank gun firing M86 APCBC. I am comparing the actual testing data for the projectile with the ToWs penetration data. I have assumed that the games penetration data for the M86 represents penetration at 0-degree obliquity.

As you can see from the first graph, the ToW M86 data is a bit skewed from what one normally sees for performance of this projectile.

I pressed on with back-calculation of the ToW slopes effects, but the results are very odd. When determining slope effects for a projectile from proving ground data, one will tend to see some statistical slop, but the general trend for full caliber AP-shot and AP-shell will always be increasing slope effect with increasing t/d. They are directly proportional. In the second graph I show actual slope effects as determined from ballistic testing of the M86 projectile (actual test results shown in red). There is a bit of scatter in the data as one would expect, but the trend is one of increasing slope effect with increasing t/d.

I have also included Lorrin Bird’s average APCBC slope effect – shown by the blue curves. These blue curves are of course generalized slope effects and represent Lorrin's averaging of a large number of APCBC projectiles. Again, the thing of importance to note here is the increase in slope effects as t/d increases.

The ToW slope effects for this projectile are represented in yellow. These were calculated by utilizing the ToW listed data for the 57mm M86. I than utilized the projectiles actual performance at 20-degrees and 30-degrees to back-calculate the games slope effects. For example:

ToW Data: 57mm M86 APCBC penetration @ 0-deg @ 100-meters = 94mm of RHA

Actual 57mm M86 APCBC penetration data @ 20-deg @ 100-meters = 89mm of RHA

Actual 57mm M86 APCBC penetration data @ 30-deg @ 100-meters = 79mm of RHA

t/d = 94/57 ~ 1.65

Slope Effect @ 20-deg = 94/89 ~1.056

Slope Effect @ 30-deg = 94/79 ~1.190

Slope Effect Assuming Simple Cosine Relationship would be a constant at all t/d ratios and would be:

@ 20-deg ~1.064

@ 30-deg ~1.155

The trend in the ToW slope effects for this projectile is of course completely opposite of what one should expect. Moreover, the yellow ToW slope effects curves represent a decreasing trend in slope effect as t/d increases. This is obviously rather contrary to how this type of projectile should be expected to perform.

Best Regards

Jeff Duquette

[ June 07, 2007, 07:38 AM: Message edited by: Jeff Duquette ]

[Jeff Duquette]

Sorry – the above doesn’t help you with making the new tank. Here are 0-degree Obliquity perforation values for 50mm L42 firing APC:

100meters = 73mm of RHA

500meters = 59mm

1000meters = 45mm

1500meters = 34mm

2000meters = 26mm

[Oudy]

Thanks for your insights and data Jeff. The slope effect I came up with by analyzing the data from the long 50mm gun was:

50mm. Kw.K.39 L/60 (APC Pzgr39 ammunition)

(first penetration number is in-game figure)

100m 80/69 1.159

500m 68/59 1.152

1000m 54/47 1.149

1500m 42/37 1.135

2000m 30/?

2500m 23/?

3000m 17/?

I just wasn't sure if the slope effect varied from different caliber guns or not. Should this number be the same throughout the ranges, or should it vary like it does? As you can tell, I haven't the slightest idea of what I'm talking about. I was just trying to make the figures for the short 50mm gun roughly match the in-game figures.

Do you think the rate of fire would be the same for both the short and long 50mm gun?

Only slightly confused,

Oudy

[Kharnvor]

Originally posted by Oudy:

Kharnvor

I assumed that as well, but when I looked at the reload rate for different 75mm guns they were different, so I just wanted to verify for accuracy.

Oudy

I realize now, since you mention some are different, that reload time is dependent not only on the size of the projectile (my basic assumption), but ammunition stowage, clearance behind the breech, the breech construction, auto- or semiauto breech, crew layout, and maybe some other factors which may have changed from version to version.

Sorry I wasn't very helpful.

I've been reading in a few threads now that gun performances may not be as accurate as possible, although Battlefront did audit the values using their best sources. So are the values being compared the ones actually used by the calculations, or are they encyclopedia values? If they are in-game values, did Battlefront really make the mistakes?

[Jeff Duquette]

Originally posted by Oudy:

Thanks for your insights and data Jeff. The slope effect I came up with by analyzing the data from the long 50mm gun was:

50mm. Kw.K.39 L/60 (APC Pzgr39 ammunition)

(first penetration number is in-game figure)

100m 80/69 1.159

500m 68/59 1.152

1000m 54/47 1.149

1500m 42/37 1.135

2000m 30/?

2500m 23/?

3000m 17/?

I just wasn't sure if the slope effect varied from different caliber guns or not. Should this number be the same throughout the ranges, or should it vary like it does? As you can tell, I haven't the slightest idea of what I'm talking about. I was just trying to make the figures for the short 50mm gun roughly match the in-game figures.

Do you think the rate of fire would be the same for both the short and long 50mm gun?

Only slightly confused,

Oudy

Hi Oudy:

Real slope effects (SE) should vary as a function of t/d -- t/d being simply the ratio of plate thickness (t) to the projectile diameter (d). If we hold projectile diameter constant, slope effect will increase as plate thickness increases. A thicker plate inclined at 30-degrees will have a greater advantage from slope effects than a thinner plate inclined at 30-deg. Sounds pretty obvious in the sense that a thicker plate should resist more cause' it's thicker. But the added advantage of higher t/d oblique impacts is of course above and beyond the simple advantage of a thicker plate vs. a thinner plate.

As to the caliber thing, I wouldn't worry too much about this level of detail given the caliber of guns in the game. You are of course technically correct in that there are scale effects involved with rigid projectile penetration of steel projectiles vs. steel armor. Larger caliber shot and shell will penetrate more efficiently at the same t/d than smaller caliber AP-shot or AP-shell. In other words, a 37mm APC shell tested against a t/d = 1 target will require more energy to perforate the target plate than a battleship's 15" APC shell fired against a t/d = 1 target. But as I say, I wouldn’t worry about the level of error this introduces as it is relatively small given the gun calibers in the game. There are larger sources of error that make this level of slop relatively insignificant.

As to the range thing and variations you are seeing in your calculated t/d values, if you hold plate thickness constant and projectile diameter constant, the slope effect will remain constant as well. What you are seeing in the variation of SE with range is the plate thickness is varying -- both the 0-degree thickness value and the 30-degree thickness value are changing at each range interval of interest. The t/d is also dropping with increasing range. For example take your values at 100meters and 1000meters range:

100m 80/69

1000m 54/47

t/d for the 100meter range target is 80/50 = 1.6

t/d for the 1000meter range target is 54/50 = 1.08

We are holding obliquity constant at 30-degrees. We should therefore expect the thicker plate (the 100meter range target with a t/d=1.6) to have a greater advantage over the attacking projectile than a thinner target. In other words the slope effect for the thicker target should be higher than that of the thinner target (the thinner target being the 1000meter range target with t/d=1.08). Examining your calculations of SE based upon the 50mmL60 we in fact see that your slope effects do make physical sense. Your numbers were:

t/d = 1.6, SE = 1.159

t/d = 1.08, SE = 1.149

1.159 > 1.149

What I would probably use for 30-degree obliquity SE for APC\APCBC would be as follows:

SE = 0.0854Ln(t/d) + 1.2695

SE = Slope Effect for 30-degree Obliquity

t/d = plate thickness divided by plate diameter

Ln: is of course natural log

For example:

t= 50mm

d= 50mm

t/d = 1

SE = 1.2695 (or 1.27 is fine)

These are average slope effects for APC\APCBC. They are not unique to specific foibles of a given projectile, but they are reasonably good for game purposes and should let you convert 30-degree penetration data to 0-degree data. Best results are bounded by t/d = 0.25 and t/d = 1.7. You can extrapolate a bit as long as you don’t stray too far east or west of the above t/d boundary conditions. Another boundary condition is that the function will not yield reasonable results for APBC or AP or subcaliber penetrators.

So yes you should see a variation in SE with range – but not because of the range itself – if you get my meaning. You see the contrast only because plate thickness and t/d will vary with range. This is a function of how penetration data is typically presented in mass consumption reference materials -- ala Jentz, Chamberlain, Hunnicutt, etc. I think it is easier for folks to understand penetration data in this format, or maybe we have just grown accustomed to seeing penetration data in this very watered down format. Real ballistic testing data is invariably presented in terms of limit velocity or limit obliquity and failure criteria. There are many more advantages to discussing plate perforation in terms of limit velocity or limit obliquity, but that is perhaps something more appropriate for another discussion.

I think your approach of using the 50mmL60 data to back out the L42 data is very logical and probably the best and most valid approach to the question. Much better than my initial approach of looking at 57mm M86.

The problem as I see it may be rooted in how the game designers are dealing with slope effects. But I need to plug and chug through some additional examples to make sure the 57mm M86 example isn't simply some weird outlier.

Best regards

Jeff

P.S. I’ll see if I have something laying about on ROF for the L42.

[Oudy]

Thanks again Jeff

I can actually follow your discuss (much to my surprise since it's been a long time since I had a math course). I pretty much figured that all of the mass produced data was simplified. It's kind of like the difference in answers you would give to a freshman vs. your colleagues.

All the best

Oudy

[Jeff Duquette]

Oudy:

Sprengrante muzzle velocity for the 50mmL42 was 450m/s. Weight of the spgr shell is listed as 1.85Kg. Bursting charge is pretty much the same as the L60 so effective fragmentation between the two guns spgr rounds is probably a wash (same).

There are a couple errors in the games listed data that I spotted while plugging and chugging. There should be no difference in weight between the pzgr-39 APC projectiles for the 50mmL42 and 50mmL60 guns. They should both be 2.06Kg. My game shows the L60’s pzgr-39 weight as 2.08kg.

I couldn’t find any information on rate of fire for either the L42 or L60. The L42 pzgr-39 cartridge is of course lighter and perhaps 5 or 6 inches shorter than the L60 pzgr-39 cartridge. I suppose in theory, this would allow a loader to load a bit quicker. Although loading rate is also a function of the ready rack arrangements, amount of room in the fighting compartment, etc. Firing rate is often more related to the gunner and his ability to lay the gun on its target than the speed of the loader. I think it would be reasonable to leave the rate of fire the same as that of the L60; or it is also probably reasonable to increase the rate of the L42 over that of the L60 by perhaps 1 or 2 rounds a minute. What is the game’s listed ROF for the L60?

I also dug around a bit more in my bookshelves and these are the more typical penetration figures one comes across for pzgr-39 fired by both the L42 and L60.

50mmL42 firing pzgr-39 @ 0-degrees

100meters = 73mm of RHA

500meters = 59mm

1000meters = 45mm

1500meters = 34mm

50mmL42 firing pzgr-39 @ 30-degrees

100meters = 53mm of RHA

500meters = 43mm

1000meters = 32mm

1500meters = 24mm

50mmL60 firing pzgr-39 @ 0-degrees

100meters = 95mm of RHA

500meters = 78mm

1000meters = 57mm

1500meters = 35mm

50mmL60 firing pzgr-39 @ 30-degrees

100meters = 67mm of RHA

500meters = 57mm

1000meters = 44mm

1500meters = 34mm

Sources can vary by a couple mm’s here and there.

As you indicated above the ToW data for the 50mmL60 pzgr-39 are as follows:

50mmL60 firing pzgr-39 @ 0-degrees

100meters = 80mm of RHA

500meters = 68mm

1000meters = 54mm

1500meters = 42mm

These are of course much lower than what one normally sees for the 50mmL60. However, it appears to me that ToW 50mmL60 figures are based upon typical perforation values one sees for the L60 @ 30-degrees and subsequently bumped up to the 0-degree values by using a uniform slope effect multiplier of about 1.2 for 30-degree obliquity. For example the figures I reported above for the L60 are from the Dattenblatte for the 50mm KwK-39 L60 firing pzgr-39. These are also consistent with the figures reported by Jentz in “Tank Battles in N. Africa”. Which probably implies Jentz got his numbers from the original Dattenblatte for the 50mm KwK-39 L60.

For example Jentz & the Dattenblatte figures for 50mm KwK-39 L60 firing pzgr-39 at 30-degrees multiplied by 1.2 are:

50mm KwK-39 L60 firing pzgr-39 @ 0-degrees.

67mm x 1.2 = 80.4mm

57mm x 1.2 = 68.4mm

44mm x 1.2 = 52.8mm

34mm x 1.2 = 40.8mm

These look reasonably close to the ToW values for the L60 -- close enough for government work and computer games.

While the merit of using a uniform 1.2 slope effect multiplier for 30-degree is questionable or debatable, it is in fact consistent with at least one simplistic German wartime method for estimating penetration at 0-degree from 30-degree penetration data. To maintain consistency within the game I guess I would tend to run with the games slope multiplier rather than using a more rigorous approach to determining slope effects for the 50mm KwK L42. Moreover, I would simply take the figures for the L42 at 30-degrees and multiply them by 1.2 to obtain the 0-degree values.

50mm KwK L42 firing pzgr-39 @ 0-degrees via ToW slope effects method.

100meters: 53mm x 1.2 = 63.6mm

500meters: 43mm x 1.2 = 51.6mm

1000meters: 32mm x 1.2 = 38.4mm

============

I spotted an unrelated an error in the Tiger-1’s listed muzzle velocity for pzgr-39. The game lists Mv as 733m/s. Jentz lists Mv = 773m/s for pzgr-39. The Schusstafeln for KwK-36 lists Mv = 780m/s for pzgr-39. Whether this make any difference to game play or not would be a function of what the actual games files are using and how (if at all) it is using Mv.

Best Regards

Jeff

[ June 09, 2007, 12:26 PM: Message edited by: Jeff Duquette ]

[Oudy]

Jeff

Thank you very much for your hard work. I really appreciate it. Hopefully, I'll be able to create an accurate version of the short 50mm thanks to you.

The game had the reload rate for the L/60 at 3.28 seconds. I lowered it to 3.00 seconds for the L/42. That gives the gun 20 shots per minute, which is about 2 shots per minute more than the L/60.

Oudy

[bus]

Here is a link to data on German guns

http://gva.freeweb.hu/weapons/germany.html#index

[John Kettler]

Oudy,

There was an extensive discussion (raging, actually) of 5 cm. APHE performance vs 2 pdr. on the CMAK Forum. Jeff had some absolutely stellar material on the 5 cm projectile family. Von Senger & Etterlin's GERMAN TANKS OF WORLD WAR II normally has a wealth of material, but unfortunately lists only one penetration number in Appendix 3, page 209 for the 5 cm L/42. That number is 56mm of armor at 60 degree slope, at 457m range. If you own CMAK or CMBB, both feature the tank in question, and much useful material may be gleaned

from the data placards for same. I suspect the Panzer Elite types may also have a mod out by now, but it's been years since I last checked.

Jeff Duquette,

Great to see you in your grog glory!

bus,

Dave Honner's site is a marvel, and he's a great guy. Corresponded with him back when some of us were accurizing Panzer Elite.

Regards,

John Kettler

[John Kettler]

Oudy,

Panzer III ammo stowage info. Both examples are carrying loose rounds as noted for combat sustainability. Designed stowage is 99 rounds.

http://www.lonesentry.com/articles/ttt07/panzer-ammunition-loads.html

From the left, Cartridges 2 and 3 are for the L/42 and L/60 5 cm guns.

http://www.quarry.nildram.co.uk/tankger.jpg

Shot's from the amazing Cannons, Machine Guns and Ammunition site.

http://www.quarry.nildram.co.uk/index.htm

Even if you can't read Polish, I believe you'll find the table useful.

http://klub.chip.pl/krzemek/pzkpfw_iii/pzkpfw_iii_uzbr.htm

Comparison of a bunch of German guns.

http://www.panzernet.net/panzernet/stranky/ruzne/kanony.htm

German derived, translated penetration table from Battlefield.ru

http://tinyurl.com/27ss2e

Regards,

John Kettler