rexford Posted January 8, 2001 Share Posted January 8, 2001 The DeMarre equation has been around a long time, and is generally accepted as a reasonable way to estimate the penetration of rounds at different velocity to predict an unknown projectile penetration from a known penetration for a different size round of the same type and country. Projectiles must be reasonably consistent in national origin, construction and manufacture for DeMarre estimation, but exact consistency is not required. In the past we have used the DeMarre equation successfully with American, British and Russian projectiles, and DeMarre should apply to German ammo. Using CM data for the 75mmL48 as a basis we DeMarre estimated 0m/0° penetration for 75L70, 88L56 and 88L71 and compared results with CM listing: 75L48 (750 m/s) 144mm CM and DeMarre basis 75L46 Pak 40 (793 m/s) 144mm CM 156mm DeMarre 75L70 (935 m/s) 178mm CM 198mm DeMarre (194mm if 925 m/s) 88L56 (780 m/s) 159mm CM 169mm DeMarre 88L71 (1000 m/s) 224mm CM 244mm DeMarre Since the penetration fall-off in CM with range appears to follow the standard DeMarre equation relationship: penetration proportional to velocity raised to 1.4283 power, the penetration estimates in CM for 75L46, 75L70, 88L56 and 88L71 may require re-examination since they appear to be low if the 75L48 penetration is correct. Link to comment Share on other sites More sharing options...
Panther131 Posted January 8, 2001 Share Posted January 8, 2001 hmmm...good post rexford. Keep em coming Link to comment Share on other sites More sharing options...
Croda Posted January 8, 2001 Share Posted January 8, 2001 Hate to be the ignorant one, but nice title! ------------------ WARNING! WARNING! WARNING! WARNING! - THIS SIG FILE BELONGS TO A COMPLETE FOO. MR T WOULDN'T BE SO KIND AS TO WRINKLE AN EYEBROW AT THIS UNFORTUNATE BEING. PLEASE OFFER HIS PARENTS AND COHABITANTS ALL SYMPATHY POSSIBLE. MAY BE CONTAGIOUS. CONTAINS ARTIFICIAL SWEETNER, INTELLIGENCE AND WIT. STAND WELL CLEAR AND LIGHT WICK. BY ORDER PETERNZ Damn Croda. That is one funny sig!!! must suck to be you - Hiram Sedai Link to comment Share on other sites More sharing options...
kipanderson Posted January 8, 2001 Share Posted January 8, 2001 Rexford, hi, Very interesting post, great stuff. Do pop over and take a look at the post, "German armour penetration overstated?" If you use the search engine you will find it. The search engine lists it under someone else's name, no idea why, but it was in fact by me. It covers the exact same ground as you do, but reaches different conclusions. That, of course, is what makes life interesting. If you have not read it yet you should enjoy it. We clearly have identical interests. All the best, Kip. Link to comment Share on other sites More sharing options...
aka_tom_w Posted January 8, 2001 Share Posted January 8, 2001 another Great post by Rexford very interesting -tom w Link to comment Share on other sites More sharing options...
rexford Posted January 9, 2001 Author Share Posted January 9, 2001 We had alot of British penetration charts, graphs and tables for Tiger I 88 and Panther 75 at 30°, and the penetration data was higher than any other data we had seen. We converted the British 30° penetration to 0° using slope effect vs. T/D, and Panther penetrated 190mm at 0m/0°. The Demarre for 75L70 from CM 75L48 is a little higher than 190mm, suggesting that CM for 75L48 may be a tad high. 75L48 looks overstated, others look understated. Link to comment Share on other sites More sharing options...
Jeff Duquette Posted January 9, 2001 Share Posted January 9, 2001 Interesting. I saw one of your posts several days ago regarding quality of test munitions relative to everyday production ammo. Is there some assumption being made regarding ammo quality? If so what basis would there be for this type of "fudge" factor...or is this something pulled straight from the hinie? I had thought that there were assumptions regarding production armour quaility relative to test plate quality (armor quality is perhaps somewhat off track to the original intent of your post). Link to comment Share on other sites More sharing options...
rexford Posted January 9, 2001 Author Share Posted January 9, 2001 We assumed British would have tested service rounds found on a Panther, best quality ammo for plate proof tests would normally not be available at front. Link to comment Share on other sites More sharing options...
Guest Big Time Software Posted January 9, 2001 Share Posted January 9, 2001 rexford, You used a 750m/s muzzle velocity for the 75L48 as the basis for your calculations, but this is incorrect. CM uses a 790m/s velocity for the 75L48. This ought to explain the discrepancy. Charles Link to comment Share on other sites More sharing options...
rexford Posted January 9, 2001 Author Share Posted January 9, 2001 German data shows that 75L48 was fired at 750 m/s, 75L46 Pak 40 at 792 m/s. Link to comment Share on other sites More sharing options...
Guest Big Time Software Posted January 9, 2001 Share Posted January 9, 2001 Ok this is interesting. Tom Jentz' Encyclopedia of German Tanks of World War Two lists the German 75mm L/48 as having a muzzle velocity of 790m/s. The slightly shorter L/43 has 740m/s. So my first thought is that rexford had inadvertently switched the two. However, I just spotted in Peter Gudgin's Armoured Firepower that he lists the L/48 as 750m/s (and the L/43 as 740m/s). So it appears we have a discrepancy - a disagreement between Jentz and Gudgin. I've got to eat dinner now so I can't rummage for more data at the moment. Anyone else got some sources to contribute here? CM currently uses the 790m/s value for the L/48 so that explains what rexford saw. If there is an error (and there may not be) it's in the 790 value, not the underlying system. My guess is that the 790m/s value makes more sense given that it's a fair bit longer than the L/48, and it's sensibe that the extra barrel length would impart more than just +10m/s. +50 seems more reasonable (740 to 790 rather than 74- up only to 750). But that is just my conjecture. Charles [This message has been edited by Big Time Software (edited 01-08-2001).] Link to comment Share on other sites More sharing options...
rexford Posted January 9, 2001 Author Share Posted January 9, 2001 German projectile data sheet for 75L48 lists 750 m/s, which is what we use. 75L46 Pak has shorter barrel but may have had more powder charge, which is how we explain things. However, PzKpfw IVH turret ring not designed for large recoil forces, which limited the muzzle velocity of 75mm projectiles. Maybe 75L43 and 75L48 had reduced powder charges to safeguard turret ring and 75L46 had normal charge. German penetration figures appear to be resolved by treating listed 75L48 penetration as really at 792 m/s (revision for 750 m/s would lower figures): If 75L46 penetrates 144mm at 0m/0° and 792 m/s, then DeMarre for 0° and 0m has: Panther 75mm penetrates 182mm at 935 m/s, 88L56 penetrates 157mm at 780 m/s, 88L71 penetrates 226mm at 1000 m/s. Above figures for 88L56 and 75L70 are German muzzle velocities. The above DeMarre estimates may be slightly different from current CM figures at range. PzKpfw IVG had 30mm face-hardened on top of 50mm face-hardened, CM lists 73mm armor which may be low. Many WW II tanks had sad turret front and mantlet armor (PzKpfw IVH, IS-2m, Pershing, M4A3E8, etc.), and weak armor was due to turret unbalance due to gun weight. Potapov article on IS tanks states that 122mm gun threw turret out of balance, and limited armor that turret front could carry. Link to comment Share on other sites More sharing options...
Guest Andrew Hedges Posted January 9, 2001 Share Posted January 9, 2001 FWIW, my German Army Handbook gives the PaK 40 (which is a 75mm L/48) a muzzle velocity of 792 m/s. I assume that the PaK 40 75mm L/48 (which is the AT gun) is very, very similar to the KwK 40 75mm L/48 tank gun. But I don't know if they are identical. Nor do I know how reliable the German Army Handbook (W.J.K Davies) is. But wait! My ancient German Tanks of WWII (v. Senger und Etterlin; that's one name) makes the PaK 40 an L/46 (not 48), but gives it the muzzle velocity of 792 m/s. However, it gives the KwK 40 L/48 750 m/s muzzle velocity. Which is non-intuitive, but there you go. Take your pick. Edited to add v. Senger u. Etterlin stuff. [This message has been edited by Andrew Hedges (edited 01-08-2001).] Link to comment Share on other sites More sharing options...
rexford Posted January 9, 2001 Author Share Posted January 9, 2001 If 75L46 Pak penetrates 144mm at 0m/0° and 792 m/s, then 75L48 penetrates 133mm, and 75L43 penetrates 131mm. This is fairly consistent with figures we use. Note that L43 to L48 barrel length increase only results in 10 m/s increase in muzzle velocity, + 1.3% velocity for 12% longer barrel. This may have lead authors to assume that muzzle velocities were in error and 75L48 should be 792 m/s. German data clearly indicates in several different places that 75L48 was 750 m/s at muzzle. Maybe PzKpfw IVf2 and G were first tanks to carry 75L43 and powder charge reduced, PzKpfw IVH may have had stronger ring or earlier tanks proved that hull could hold 750 m/s and charge on 75L48 increased above 75L43 but still below 75L46. Link to comment Share on other sites More sharing options...
rexford Posted January 9, 2001 Author Share Posted January 9, 2001 Germans may have referred to 75L48 anti-tank gun as 75L46 to avoid confusion, with tank gun listed as 75L48. Link to comment Share on other sites More sharing options...
Jeff Duquette Posted January 9, 2001 Share Posted January 9, 2001 A little confusion here. I thought Rexford was saying the 75mmL48 using 750m/s was predicating comparable penetration values to DeMarre EQ’s. Both CM and DeMarre @ 144mm. Then an explanation is put forth to explain a “discrepancy” problem in actual muzzle velocity employed by Rex. CM uses 790m/s and Rex used 750m/s. If the velocity were jacked up to 790m/s than DeMarre and CM would not agree. So in essence CM’s 75L48 is under-predicating penetration relative to DeMarre. This is consistent with all the other comparisons presented by Rex (L70, L56 and L71). Just to throw an additional monkey wrench into the equation…not that I would put a huge amount of faith in the following…but what the heck. From US War Department “Handbook on German Military Forces, 1939 – 1945” 75L48 is listed as having a muzzle velocity for APCBC of 2,300 fps. This muzzle velocity is mentioned in several areas in the text with respect to different vehicles mounting the L48. 75L70 is rated at 3,068 fps for APCBC. This one at least checks out well with other sources. 88L71 is rated at 3,280 fps for APCBC. This one also checks out relative to other sources as well. I can’t find a rating or even a listing of L46. L43 is pretty common. Regarding Ammo quality…thanks for the reply Rex. Sounds like common production ammo is not attributable to the contrasts in DeMarre and CM penetration values. Link to comment Share on other sites More sharing options...
PzKpfw 1 Posted January 9, 2001 Share Posted January 9, 2001 <BLOCKQUOTE>quote:</font><HR>Originally posted by Big Time Software: Ok this is interesting. Tom Jentz' Encyclopedia of German Tanks of World War Two lists the German 75mm L/48 as having a muzzle velocity of 790m/s. The slightly shorter L/43 has 740m/s. onjecture. Charles ]<HR></BLOCKQUOTE> IIRC the Encyclopedia of German Tanks of World War Two was not written by Tom Jentz; he was the editor, his long time comrades, Chamberlin & Doyle were the authors, again this is IIRC I'm to tired to dig the book out presently. As for Jentz himself, he lists the 7.5 cm KwK.40 L/48 firing PzGr.39 with an initial MV of 740/ms in Panzer Truppen Vol 2 P. 296. The British in their wartime report, Table V: 7.5cm Ammunition Penetration list the 7.5 cm KwK.40 L/48 fireing PzGr.39 with an MV of 750m/s & the 7.5 cm Pak 40 L/46 fireing PzGr.39 with an MV of 792m/s Regards, John Waters ------------------ "We've got the finest tanks in the world. We just love to see the German Royal Tiger come up on the field". Lt.Gen. George S. Patton, Jr. February 1945. [This message has been edited by PzKpfw 1 (edited 01-08-2001).] Link to comment Share on other sites More sharing options...
Guest Big Time Software Posted January 9, 2001 Share Posted January 9, 2001 Tom Jentz is the "technical editor" of Encyclopedia of German Tanks of World War Two. I take that to mean that he would be largely responsible for things like armor penetration tables, and in that book it's stated that the L/48 has a muzzle velocity of 790 m/s. It may not be correct. Jentz' Panzer Truppen actually lists the L/43 and L/48 on the same line in the chart, as if there is no difference at all between them. In my opinion that makes this particular reference suspect. There should be some difference between the L/43 and L/48, the question is how much. Well, we've dug through our library and it appears that the Jentz Encyclopedia reference mentioned above is the only one that lists 790m/s as the velocity for the KwK40 75mm L/48. Given that several other sources say it's 750 m/s I think I will make the change to 750 m/s. I hate to throw out data from a figure as respected as Tom Jentz, but it looks like he may have got this one wrong. If anyone has further light to shed on this, please let me know. I do wonder why the L/48 increased muzzle velocity to such a small extent over the L/43. Perhaps a smaller propellant charge is the culprit, as rexford suggested. Jeff - rexford was assuming that CM's 75mm L/48 used a muzzle velocity of 750m/s, and so to him the penetration figures looked strangely high. But really what happened is that CM rates the L/48 at 790m/s, which now appears to be incorrect. When we reduce it to 750m/s the figures should line up. Charles Link to comment Share on other sites More sharing options...
PzKpfw 1 Posted January 9, 2001 Share Posted January 9, 2001 <BLOCKQUOTE>quote:</font><HR>Originally posted by Big Time Software: Tom Jentz is the "technical editor" of Encyclopedia of German Tanks of World War Two. I take that to mean that he would be largely responsible for things like armor penetration tables, and in that book it's stated that the L/48 has a muzzle velocity of 790 m/s. It may not be correct. Charles<HR></BLOCKQUOTE> Charles I agree that Jentz being listed as TE implys he had a hand in the compilation but; he was not the author; & refering to him as the author is incorrect in that sense. One could contact Hillary Doyle & bring the L/48 MV discrepency to his attention & ask for a comment. The British wartime Table V: 7.5 cm Ammunition Penetration chart lists the 7.5 cm KwK.40 L/43 fireing PzGr.39 with an MV of 740m/s. I'd also reccomend getting: German Explosive Ordnance (Projectiles and Projectile fuses) March, 1953, NTIS call number ADA376695 it lists all known technical parameters of every German projectile. With cut-away drawings for each projectile. it was an compilation of the wartime U.S. Captured Ammunition Bulletin series, and the British Handbook of Enemy Ammunition Pamphlet series. Regards, John Waters ------------------ "We've got the finest tanks in the world. We just love to see the German Royal Tiger come up on the field". Lt.Gen. George S. Patton, Jr. February 1945. [This message has been edited by PzKpfw 1 (edited 01-09-2001).] Link to comment Share on other sites More sharing options...
Jeff Duquette Posted January 9, 2001 Share Posted January 9, 2001 <BLOCKQUOTE>quote:</font><HR>Steve Said: Jeff - rexford was assuming that CM's 75mm L/48 used a muzzle velocity of 750m/s, and so to him the penetration figures looked strangely high. But really what happened is that CM rates the L/48 at 790m/s, which now appears to be incorrect. When we reduce it to 750m/s the figures should line up.<HR></BLOCKQUOTE> Je vois. Merci de cette clarification. Peut-être à l'avenir je devrais lire tout le poteau de Rexford. Je Mauvais Link to comment Share on other sites More sharing options...
Slapdragon Posted January 9, 2001 Share Posted January 9, 2001 <BLOCKQUOTE>quote:</font><HR>Originally posted by Jeff Duquette: Je vois. Merci de cette clarification. Peut-être à l'avenir je devrais lire tout le poteau de Rexford. Je Mauvais <HR></BLOCKQUOTE> Ne devenez pas fou maintenant. Vous ne voudriez pas commencer une mauvaise habitude. Link to comment Share on other sites More sharing options...
Guest Big Time Software Posted January 9, 2001 Share Posted January 9, 2001 Hehe... and Jeff, while you are at it give credit where credit is due. Charles helped you out there, not me When things get technical like this, I grant Charles "permission" to post instead of coding Steve Link to comment Share on other sites More sharing options...
rexford Posted January 9, 2001 Author Share Posted January 9, 2001 It appears that our data was based on von Senger after reviewing other published studies. 75L48 at 750, 75L46 Pak at 792 is what our data is based on. Link to comment Share on other sites More sharing options...
Jeff Duquette Posted January 9, 2001 Share Posted January 9, 2001 <BLOCKQUOTE>quote:</font><HR>Slap Said: Ne devenez pas fou maintenant. Vous ne voudriez pas commencer une mauvaise habitude.<HR></BLOCKQUOTE> Fou? Je fais le vent de la mauvaise odeur dans votre general direction. <BLOCKQUOTE>quote:</font><HR>Steve Said Hehe... and Jeff, while you are at it give credit where credit is due. Charles helped you out there, not me When things get technical like this, I grant Charles "permission" to post instead of coding <HR></BLOCKQUOTE> Ahhh... Charles. L'homme caché par le rideau. Le magicien de armor penetration. Link to comment Share on other sites More sharing options...
Guest Big Time Software Posted January 9, 2001 Share Posted January 9, 2001 Hehe... I didn't even need to do translations at Babelfish for that last post Jeff. Especially the one aimed in the "general direction" of Slapdragon Steve Link to comment Share on other sites More sharing options...
Recommended Posts