rexford

The "L" represents the length from the breech to the end of the barrel, and does not include muzzle brake length. The point on the breech block where the measurement started varied from country to country, I think the Sherman 75mm L40 gun designation actually works out to 75mm L37 in the British system, but I could be wrong. I'll look for the really good explanation that showed up on the Russian Battlefield site some time ago. The 75mm L46 German anti-tank gun fired 6.8 kg APCBC rounds at 792 m/s while the 75mm L48 tank gun fired the same round at 750 m/s. The 75mm L46 APCBC shell casing was much longer than the L48 due to more powder charge in the L46 ammo. The German 75mm L70 fired the 6.8 kg APCBC ammo at 935 m/s. Higher muzzle velocity means flatter trajectory which results in less of an error (measured from aim point) for a given range estimation error. If the 75mm L48 and 75mm L70 fire APCBC at a 2m x 2m target and both use the correct range setting (target at 1000m, both guns set for 1000m shot), more 75mm L70 shots will hit since it had a much smaller constant aim random scatter than 75mm L48, as shown in firing tests.

The 90mm guns were firing downward on the Panther, although I don't remember the angle. At close range, 90mm T33 APBC (a modified version of 90mm M77 AP with a harder nose and a windscreen) could penetrate the Panther glacis on level ground beyond 1000 meters. 90mm M77 AP could penetrate the Panther glacis on level ground at close range, too. 90mm APCBC wouldn't be expected to penetrate the Panther glacis very much at any range unless the armor was very poor and there was a considerable downward angle to the shot. I do not remember if the firing tests included 90mm HVAP ammo. Robert Livingston has our copy of the full report with pictures, I can ask him for more details if you are interested.

The first picture in this thread is from the December 1944 firing tests conducted by the Americans with a variety of 90mm ammunition. From what Robert Livingston found, the tests took place a day or two before the Battle of the Bulge start. [ October 23, 2003, 06:43 PM: Message edited by: rexford ]

The German 75L43 fired 6.8 kg APCBC projectiles at 740 m/s muzzle velocity, the 75L48 at 750 m/s and the 75L46 at 792 m/s, so the L46 would penetrate the most and the L43 the least. Penetration is roughly proportional to the velocity raised to the 1.43 power when the projectile weight and diameter are equal. The Russian 76.2mm L51.5 used in a Marder fired a 7.6 kg APCBC projectile at 710 m/s.

SU 85 front hull is at 50 degrees from vertical, T34 is at 60 degrees, which makes a big difference in terms of effective resistance.

U.S. Field Manual FM 17-12, dated April 22, 1943, informs Stuart and Sherman crews that: 1. Do not use 37mm armor piercing ammunition beyond 500 yards 2. do not use 75mm armor piercing ammunition beyond 2000 yards 3. for tank targets beyond 2000 yards, use 75mm HE since a hit on the track will disable the tank and fragmentation from near misses harasses the crew. Interesting limitation on use of 37mm AP and APCBC, wonder how many crews in field disregarded the manual. With regard to HE use, the manual states that "Do not use the tank gun against a target when the machine guns can handle it."

FM 17-12 presents some interesting advice on the use of the Sherman gyro stabilizer: "FIRING WHILE MOVING" "Firing with the 75mm gun while moving is inaccurate and causes an uneconomical expenditure of ammunition. Do it only in an emergency and at ranges of 600 yards or less." Even with a gyro stabilizer 600 yards is about it, and misses are expected. The 600 yard range may be based on a reasonable hit probability given the initial range estimation (which may contain some error), and the small angle errors that will occur with a stabilizer. "Firing while moving requires close teamwork between driver and gunner. Drive at a constant speed: acceleration and decleration upset the action of the stabilizer. Drive in a straight line, otherwise the gun yaws as the tank turns. When going over rough terrain, do not fight the gun (attempting to keep it on target by spinning the elevating handwheel) but wait until a constant speed and regained and the action of the stabilizer has smoothed out." Gyro stabilizer needs flat even surfaced terrain. "The stabilizer will not lay the gun. It merely tends to keep the gun where it has been laid: that is, it eliminates extremely jerky movements caused by the movement of the tank. Even with a stabilizer, the gun does not hold constantly on the target. Watch the swing of the gun through the target and fire as the proper sight setting crosses the target." It's not as simple as laying the gun on the target and then firing away. It's kind of like shooting at a moving target, except one has to wait for the target to enter the crosshairs and then quickly get off the shot.

FM 17-12 presents some interesting advice on the use of the Sherman gyro stabilizer: "FIRING WHILE MOVING" "Firing with the 75mm gun while moving is inaccurate and causes an uneconomical expenditure of ammunition. Do it only in an emergency and at ranges of 600 yards or less." Even with a gyro stabilizer 600 yards is about it, and misses are expected. The 600 yard range may be based on a reasonable hit probability given the initial range estimation (which may contain some error), and the small angle errors that will occur with a stabilizer. "Firing while moving requires close teamwork between driver and gunner. Drive at a constant speed: acceleration and decleration upset the action of the stabilizer. Drive in a straight line, otherwise the gun yaws as the tank turns. When going over rough terrain, do not fight the gun (attempting to keep it on target by spinning the elevating handwheel) but wait until a constant speed and regained and the action of the stabilizer has smoothed out." Gyro stabilizer needs flat even surfaced terrain. "The stabilizer will not lay the gun. It merely tends to keep the gun where it has been laid: that is, it eliminates extremely jerky movements caused by the movement of the tank. Even with a stabilizer, the gun does not hold constantly on the target. Watch the swing of the gun through the target and fire as the proper sight setting crosses the target." It's not as simple as laying the gun on the target and then firing away. It's kind of like shooting at a moving target, except one has to wait for the target to enter the crosshairs and then quickly get off the shot.

Just came across the subject site at: http://www.usswashington.com/dl_index.htm Reading through the October 18-24, 1942 presentation there are some good tidbits on Russian snipers at Stalingrad and PzKpfw IIIJ-vs-Sherman in Africa.

Had nothing to do with your post, I just thought it was interesting.

The sight diagram for M3 75mm gun with telescopes M32, M38 or M55 has this relationship between CAL .30 AP MG bullets and SHOT A.P. M61 for the same elevation angle: M61 APCBC 600 yards, coax MG 700 yards M61 APCBC 1000 yards, coax MG 1000 yards M61 APCBC 1500 yards, coax MG 1200 yards M61 APCBC 2000 yards, coax MG 1400 yards M61 APCBC 2500 yards, coax MG 1600 yards M61 APCBC 3000 yards, coax MG 1800 yards Gun elevation angle increases as one heads down the sight. Setting the 75mm gun for an M61 APCBC shot to 2000 yards uses the same elevation angle as the coax MG firing at a 1400 yard target. With coax MG range estimation, roll the MG bullets until they fall onto the target and note the range on the MG sight markings. Say it is 1200 yards. Since one estimates the target range to be 1200 yards based on the coax MG, a shot with M61 APCBC would then use an elevation for that ammo which results in a 1200 yard shot. And the 75mm M61 APCBC shot against a target range of 1200 yards would result in a gun elevation angle less than the coax MG at the same range. [ October 08, 2003, 08:22 PM: Message edited by: rexford ]

The sight diagram for M3 75mm gun with telescopes M32, M38 or M55 has this relationship between CAL .30 AP MG bullets and SHOT A.P. M61 for the same elevation angle: M61 APCBC 600 yards, coax MG 700 yards M61 APCBC 1000 yards, coax MG 1000 yards M61 APCBC 1500 yards, coax MG 1200 yards M61 APCBC 2000 yards, coax MG 1400 yards M61 APCBC 2500 yards, coax MG 1600 yards M61 APCBC 3000 yards, coax MG 1800 yards Gun elevation angle increases as one heads down the sight. Setting the 75mm gun for an M61 APCBC shot to 2000 yards uses the same elevation angle as the coax MG firing at a 1400 yard target. With coax MG range estimation, roll the MG bullets until they fall onto the target and note the range on the MG sight markings. Say it is 1200 yards. Since one estimates the target range to be 1200 yards based on the coax MG, a shot with M61 APCBC would then use an elevation for that ammo which results in a 1200 yard shot. And the 75mm M61 APCBC shot against a target range of 1200 yards would result in a gun elevation angle less than the coax MG at the same range. [ October 08, 2003, 08:30 PM: Message edited by: rexford ]

The following tidbits suggest that smoke was not available for the Sherman 75mm gun during the African campaign, and coaxial machine guns were used to an unknown degree for range estimation: Sherman Field Manual FM 17-12 indicates for "SMOKE SHELL" that "Smoke shell for tank guns is under development. The smoke shell now issued for the 81-mm mortar is very effective for screening. (See FM 17-27.)" The date of the FM 17-12 is April 22, 1943. The gun sight for Sherman 75mm in FM 17-12 includes range markings for SHELL SMOKE (WP) MK II, with a maximum range of 2200 yards. FM 17-12 has a section on "DETERMINATION OF RANGE, a. Estimation by Eye" which suggests use of the coaxial machine gun for range estimation by Shermans. "By firing a coaxial machine gun - Fire the machine gun with an estimated range and roll the strike into the target. The point on the reticle at which the strike appears is the range setting for the machine gun. Refer to the sight diagram and determine the corresponding range setting for the tank gun."

The following tidbits suggest that smoke was not available for the Sherman 75mm gun during the African campaign, and coaxial machine guns were used to an unknown degree for range estimation: Sherman Field Manual FM 17-12 indicates for "SMOKE SHELL" that "Smoke shell for tank guns is under development. The smoke shell now issued for the 81-mm mortar is very effective for screening. (See FM 17-27.)" The date of the FM 17-12 is April 22, 1943. The gun sight for Sherman 75mm in FM 17-12 includes range markings for SHELL SMOKE (WP) MK II, with a maximum range of 2200 yards. FM 17-12 has a section on "DETERMINATION OF RANGE, a. Estimation by Eye" which suggests use of the coaxial machine gun for range estimation by Shermans. "By firing a coaxial machine gun - Fire the machine gun with an estimated range and roll the strike into the target. The point on the reticle at which the strike appears is the range setting for the machine gun. Refer to the sight diagram and determine the corresponding range setting for the tank gun."

If you're interested I'll scan some pages from the Sherman gunnery manual for 75mm ammunition and e-mail them to you direct. The manual pages on range elevation for stationary targets, and lead against moving targets are short and to the point. The tank manual for Shermans directs the crew to use machine guns against targets instead of HE if the machine gun can do the job. The 75mm weapon gun sight includes range elevations for APCBC, AP and HE, and they are all fired by lining up a target with the gun direction and then elevating the gun to the estimated range. No differences. The gun sight for 75mm Shermans may have some range elevation markings for smoke. I'll have to check. If one is firing on a target where armor penetration is needed with HE, the shell delay is set and the round explodes a certain number of seconds after contact. A 0.05 second delay can be obtained with Sherman 75mm HE, which is good against troops in cover or trenches. Aim in front of the enemy troops, bounce the round off the ground (ricochet fire) and have it explode in the air. Against anti-tank gun shields and thin vehicle armor delayed detonation of HE works best, cause you don't want the round exploding before it goes through the armor. Sherman 75mm base emission smoke was an odd round. It was useful from 800 to 1650 yards (I think this is the range, will have to check it tonight), which seems like an unusual range interval. The round was fired by aiming at and hitting the ground in front of a target and having the shell ricochet as it bounced along its path. Smoke was emitted from the base of the round as it bounced along the ground, that's why it's called base emission smoke. If the round hit the ground too close to the gun, the impact damaged the projectile and it wouldn't work well. 1650 yards was the maximum range due to the low muzzle velocity, poor ballistic shape and max elevation of the gun.

Things may be a little simpler than JasonC points out if one is talking about WW II tanks and guns. With the Sherman 75mm gun sight, you line up the stationary target so it is in the middle of the scope markings from side to side. Then you estimate range, where the average crew was able to be within 25% of the true range on about 68% of the guesses: errors range from 0% to about 100%. 88mm Flak and Nashorns may have used range finders. The Sherman gun scope has vertical range markings, so if the range is estimated to be 750 yards one raises the gun until the middle of the target is about halfway between the 500 yard and 1000 yard lines. It appears that the Sherman scope moved with the gun elevation. If the shot falls short, one can use standard bracketing procedures or elevate the gun so the target is where the shot passed it on the scope (burst on target procedure). With bracketing, if the shot falls long or short by about 200m one would add or subtract a set amount. That is how it works in training, on the battlefield all sorts of silly errors come into play due to nervousness, fatigue, fumes, heat, yelling and fear. And other stuff, too. If the target is moving across the line of sight, one tracks the vehicle by moving the gun with the target, jumps ahead of the target by the appropriate lead angle for the estimated lateral speed, and fires. Note that a target moving straight at a gun does not require a lead angle, so it not very much more difficult to hit than a stationary target.

Sherman tank 75mm HE can be set for 0.05 second delay, or superquick action with immediate detonation. U.S. manual on Tank Gunnery states that "Superquick action when striking armor plate, a gun shield or a building will burst before it can penetrate." "The 0.05 second delay action results in the shell penetrating before bursting when it strikes light armor, gun shields or buildings. If the shell strikes the ground, it ricochets, travels 20 to 25 yards beyond the point of impact, and then bursts about 10 feet in the air. Because of the downspray from the burst in tyhe air, a ricochet burst has devastating effect on personnel without overhead cover."

PzKpfw IV Universe site presents penetration against vertical armor.

Many HE shells can be set for instant detonation upon impact, or for a delay between impact and explosion. Against infantry in the woods, instant detonation works best for hits high up against trees, where you want fragments to instantly rain down on infantry under or near trees. For infantry in trenches, set HE for delay and fire at ground infront of trench so shell hits ground, bounces up in the air and explodes over the trench. I assume anti-tank use of HE shells would set detonation to delay.

The Tiger mantlet thickness is 135mm on the rounded area directly around the gun, 140mm to 150mm thick on the flat areas where the gunner vision slit and machine gun poke out, and 100mm to 125mm at the extreme top and bottom. While the tapered 100mm-to-125mm mantlet top and bottom seems to be the thinnest area, there is a 100mm plate directly in back of the area. Even with edge effects against armor piercing projectiles, the tapered top/bottom area of the mantlet is a tough nut to crack. The above thicknesses are design thicknesses taken from German drawings. If 95mm HEAT penetrates 127mm of vertical armor, the Tiger mantlet is not going to be defeated except once in a very long while.

That's a good connection that sums up what goes on. The drop-off in 75L43 penetration with range is about the same with APCBC or HE, where APCBC loses 10% of its penetration from 500m to 1000m and HE loses 11%. This suggests that impact velocity is driving penetration of both ammo types. When the HE burster inside armor piercing rounds is defective, such as on U.S. 90mm APCBC tested in England just before D-Day, the rounds detonated on the surface of the armor they hit and failed to penetrate easy targets. To penetrate successfully, the HE inside a shell or shot must not detonate until the round has passed through the armor. [ September 30, 2003, 01:55 AM: Message edited by: rexford ]

A U.S. report on Russian weapons and vehicles give hardness data for Russian HE and armor piercing rounds. Russian HE shells ranged in hardness from 180 to 250 Brinell Hardness, while the noses of the armor piercing ammo averaged about 480 Brinell Hardness. So Russian HE ammo was softer than the homogeneous armor carried by most German tanks but was still harder than regular structural steel used in buildings and bridges. As noted in a previous post by Redwolf, HE shells appear to penetrate by pushing through the armor they hit using the same mechanisms as armor piercing rounds. [ September 30, 2003, 01:49 AM: Message edited by: rexford ]

Penetration data for German 75mm L43 gun is available at PzKpfw IV Universe site: http://ourworld.compuserve.com/homepages/willphelps/Specs-03.htm Vertical penetration by 75mm L43 APCBC 126mm at 500m 113mm at 1000m HE 47mm at 500m 42mm at 1000m The HE round is fired at 550 m/s while the APCBC is launched at 740 m/s. The DeMarre equation for penetration versus velocity predicts that a round fired at 550 m/s will penetrate about 65% of the same ammo at 740 m/s. So some of the difference between HE and APCBC is due to a lower muzzle velocity. 126mm at 500m for APCBC x 0.65 = 82mm. I would guess that the difference between 82mm penetration at 500m by APCBC (if fired at 550 m/s muzzle velocity) and 47mm at 500m for HE is due to: 1. softer steel with HE rounds 2. lighter HE round (12.6 pounds for HE vs 15 for APCBC) 3. a larger HE burster cavity in the HE shell (which weakens the projectile structure so more of the impact energy is absorbed by the HE round compared to APCBC) 4. nose shape differences. So there are the differences between HE and APCBC that account for less HE penetration, plus lower muzzle velocity for 75L43 HE. Panther 75L70 fires APCBC at 935 m/s, shoots HE at 750 m/s. Tiger II 88L71 fires APCBC at 1000 m/s, rips off HE rounds at 700 m/s. Tiger I 88L56 unloads APCBC at 780 m/s and HE at 810 m/s.

Armor piercing projectiles have very hard noses and hardened shell casings, which are designed to rip through hard armor. HE shells are designed to hit something and then explode into lots of pieces shortly thereafter. My book did not go into HE penetration stats. The only HE penetration figures I've seen are German ones which Mark Diehl published in AFV-G8 maagazine a long time ago. I think but am not sure that the thin armor penetrated by HE shells is based on actual penetration of the armor by the projectile nose or body, which would have to occur fairly quickly.

Thanks John.