U.S. 75mm Penetration

[rexford]

Following web site contains U.S. firing tests for 75, 76 and 90 APCBC during 5/44, just before D-Day, with service rounds (not some high quality test job):

http://members.nbci.com/mycenius/weapons/armour4.html

Isigny tests against 3 Panthers same site, end with armour6.html

During May 44 tests, 75mm with HE burster and with inert filler were both fired at same target, round with HE inside slightly outpenetrated inert filler version. Since HE burster version heavier than inert filler, penetration difference might be due to projectile weight.

75mm penetration against 70mm @ 0° closely matches U.S. test data, suggesting that American data in TM-9-1907 is with service ammo. TM-9-1907 compares to CM data in following manner:

500m

CM 89mm

TM 82mm

100m

CM 97mm

TM 90mm

U.S. 76mm APCBC in test penetrates 100mm plate at 30° at 500 yards, which exceeds CM prediction by a bit. TM-9-1907 predicts that 76mm APCBC at 500 yards would penetrate 93mm on 50% of hits, so penetrating 100mm/30° on two hits out of two at 500 yards is on the lucky side.

76mm service round in these pre-D-Day tests did not exhibit brittle behavior and exceeded CM and TM predictions.

Firing a few rounds on one day does not answer all questions, but does raise a few questions.

There is some confusion in the May 1944 report regarding 75mm tests at 30°. Report text says 60mm at 30° in one place, chart shows 70mm at 30°. TM-9-1907 data for penetration range has 64mm at 30°.

One other issue is that 75mm APCBC did not "shatter gap" when penetration greatly exceeded 70mm/0° plate, suggesting that shatter failure on overpenetrating hits may be limited to impact velocities above 2000 fps. So "shatter gap" probably would not apply to 75L40 APCBC at most ranges, although it might at 20m or so. This needs more study.

[:USERNAME:]

Seems the report backs up that there is considerable obscuration from the blast of a US gun. Even into a wind on a dust free grassy area. Similar to the US rifle and MG problem from not having smoke free powder...

Interesting. Was there a US ammo quality problem as well as a fuze quality issue? Inquiring minds want to know..

Lewis

[Jeff Duquette]

Sorry Rexford….don’t mean to digress from the topic on yet another one of your threads . Regarding smokeless powder, the following is from “Investigations in Germany by Tank Armament Research” Ministry of Supply.

<BLOCKQUOTE>quote:</font><HR>INVESTIGATIONS IN GERMANY BY TANK ARMAMENT RESEARCH, MINISTRY OF SUPPLY

SECTION E

METHODS OF IMPROVING OBSERVATION OF FALL OF SHOT

NOTE: this section covers methods of reducing flash, smoke and dust which are produced when a gun is fired. It is desirable to reduce these factors both in order to improve the tank gunner's observation of fall of shot and also to avoid giving away the position to the enemy.

Krupp, Essen (personnel evacuated to Kettwig)

Dr. Muller said that the Waffenkommission attached considerable importance to the search for methods of reducing flash, smoke and dust. Early in the war, German tank ammunition was flashing, but there was a swing over to flashless ammunition produced by introducing potassium sulphate into the propellant. At first a fairly satisfactory combination was obtained, though flashlessness was thus achieved at the expense of some smoke. As the war progressed, propellants deteriorated badly in quality and smoke became excessive. At this stage, users said they would prefer flashing to flashless ammunition. No advantage was gained by using electric primers.

Contrary to certain reports, no change over from flashing to smoking ammunition was made for tanks in poor and fading light. Experiments were done to determine the optimum port size for muzzle-brakes, and it was considered that those for the Pak 7.5 cm. were about right.

(NOTE: T.A.R. experiments have shown that when the Pak 7.5 cm. muzzle-brake is attached to the 17-pr. gun in Challenger, the amount of forward dust raised is slightly less than with the British service muzzle-brake.)

Rheinmetall-Borsig, Dusseldorf

Propellants deteriorated as the war progressed and smoke was becoming a real nuisance. Tanks were therefore just being provided with long periscopes 1½ metres, which were stated to be quite satisfactory (My Note: This was the TSR1 monocular observation periscopes provided in Panthers. Apparently General Guderian was not particularly pleased with the TSR1, and its intended role in observing over flash, smoke and dust generated during firing of the main gun, and recommended the use of “wingman” tanks helping each other in observing fall of shot).

All tank guns were fitted with muzzle brakes, but the recoil systems were designed to stand recoil in the absence of muzzle-brakes. The effect of blast on the tank crew was always a factor considered in designing muzzle-brakes. The effect of muzzle-brakes on flash, dust and smoke was not considered. (This is at variance with statement by Krupp personnel).

Flash was considered less important as an obscuring element than smoke, even at dusk, because of its momentary duration. In any case the commander could use his long periscope. <HR></BLOCKQUOTE>