Most secondary sources on the effects of Schurzen on ATR projectiles point back to the original testing reports from Kummelsdorf in February of 1943. It was based on this test reporting that the orders for Shurzen production and fitting to Pz III and IV were given.
I have never been able to find an original of the Kummelsdorf reports online. Doesn't mean it's not there somewhere, but if it is I haven't found it.
Perhaps the most widely accredited secondary sources are the various books by Jentz. His books on Pz III, Pz IV, Panther A, and StuG III all provide information from the Kummelsdorf 2/43 testing. I do not know if the larger, more expansive "Panzer Truppen" volumes also contain details of these tests.
From reading secondary (and tertiary) sources I understand that the 2/43 tests assessed the impact of both 5mm non armor-grade plates, and wire mesh screens, on Russian 14.5mm ATRs at a range of 100m, and on 75 / 76.2mm HE rounds. It is my understanding that no other types of weapons were included in these tests.
These tests were conducted due to the fighting conditions on the Eastern Front in 1942. ATRs (both PTRS-41 and PTRD-41) had become common over the course of 1942. For larger guns there were shortages of AP production in 1942, so it was relatively common for Soviet gunners to fire HE at German tanks. The 30mm armor on the sides of Pz III and Pz IV was shown in combat to be vulnerable to both. As both models were up-armored on the front, the chassis were becoming overloaded, and up-armoring the sides to provide effective protection levels was simply not in the cards for these vehicles.
The findings were that both 5mm steel and wire mesh were effective. The effects on 14.5mm ATR projectiles was to induce wobble so that the rounds side-struck the armor behind, and failed to penetrate. The HE rounds detonated at a distance from the armor, preventing damage to both the interior of the tanks (preventing penetration or significant spalling from non-penetrating HE hits) and also reducing damage to the running gear.
As both plate steel and wire mesh were found effective, it was thought that the lower weight of the wire mesh would be a superior solution. However the lack of rigidity in the wire mesh meant that more complicated mounting mechanisms were needed. So the plate went into production immediately, and the wire mesh skirting did not go into production until more than a year later.
I have never seen a reference to primary source materials of German testing of Schurzen against hollow-charge projectiles, nor against larger AT projectiles.
However the US Army did conduct test-firings against add-on spaced armor plating as part of the Shoeburyness tests in May of 1944. These tests, conducted near Essex in the UK, were largely set up to demonstrate the enhanced firepower of the new 76mm gun mounted in 100 M4A1 Shermans that Ordnance had rushed to the UK in anticipation of the D-Day landings, and also of the new 90mm tank gun that was being mounted in upgraded M10A1 TDs (to be re-named M36) in the states in preparation for shipment to ETO. The primary interest seems to have been demonstrating against the armor levels expected in Tiger tanks -- Phase 1 firings were against 120mm plate at 30 degrees, Phase 2 were against 100mm plate at 30 degrees. But the test firings included a Phase 3 firing set against spaced armor plates ... at 50mm plates that also had a 20mm plate 6 inches in front. These Phase 3 firings demonstrated how such an arrangement could initiate the fuzing of US AP shells leading to failure against the 50mm plate, in an environment where British AP shot (solid penetrators) or even inert-filled US AP shells would penetrate completely.
However, this testing set-up does not mimic Schurzen. Rather, it appears to mimic Vorpanzer, a rarely seen German add-on armor kit produced for Pz IV with the notion of enhancing the protection of tanks that would lead assault waves against prepared defenses.
I have test results from other firing tests, such as Bazookas against Panthers, or US 37mm, 57mm, 75mm and 105mm rounds, including 105mm HEAT and 75mm HE and WP, against various test targets. But I have no primary sources for HEAT or AP projectiles against Schurzen.
The test firings of the bazooka against Panther does tend to lead one to the conclusion that just about ANYTHING between the projectile and the target plate will help defend against penetration. Wheels, tires, exhaust pipes, even tow hitches were struck by projectiles in those tests, and while bazooka rounds clearly penetrated with lethal effect when striking the armored plate cleanly on sides or rear, when they struck these various stand-off protrusions the side or rear armor was effectively protected from penetration.
Best I got, boyz. Hope it helps.
(aka: Mk 1)