Sound Suppressor for the MP40
The mp38, 40 and 41 made use of the "Blowback with advanced primer ignition (API)" system, as a consequence of which, that complete sound suppression would not be possible due to a significant portion of the blast existing the area that the 9mm round was chambered. In addition to the standard 9mm Parabellum round travels faster than 1080 feet per second.
Note: "Blowback with advanced primer ignition (API)" system implies that the round is detonated from a blow-back operated bolt/recoil system, and that the ignition of the primer at the base of the 9mm round is ignited a fraction of a second BEFORE the round is completely seated in the chamber of the barrel.
Still the Heeres Waffenamtes instructed the following firms to develop a sound suppressor:
1) Arado Flugzeugwerke GmbH, Werk Brandenburg/Havel, code: hkx
2) Schneider, Adam, AG, Maschinenfabrik,Berlin N 65, Fennstrasse 31 aod
On the 17th of February 1943 both companies presented their samples to the officials of the Heeres Waffenamt
he picture on the right shows a letter from Major Ley of the Heeres Waffenamt send to Major Heilmeyer.
It states the following:
Major Ley Berlin, 13th. of February 1943
Wa Pruf J3 - 0901 App. 112
Mr. Major Heilmeyer
Wa Staff/Command group
Subject: Telephonic meeting Major Heilmeyer - Major Ley on 13.2.1943
Regards: Sound suppressor for MP.
At this moment two samples have been developed by the company of A r a d o, Brandenburg and S c h n e i d e r - Opel, Berlin, and were presented on the 17.2 in Dahlem, Kronprinzenalle 121.
Both systems are working according to the chamber system. Contradictory to the Russian System with the rubber baffles this system has the disadvantage that the soundlevel remains a little higher. The advantage however is that the accuracy is higher.
Sound suppressor with rubber baffles for MP's have so far not lead to any useful results.
In order to disguise the project the sound suppressors were called "Haube" (Hood). In total 4 different sound suppressor were developed for the MP40:
L 41 (new version)
The newer version of the L 41 was made by Arado. I assume that the earlier L41 also was made by Arado. The L 41 had a cylindrical shape and was screwed on the muzzle. It had a diameter of 43 mm, a length of 295 mm and weight was about 0,7 kg.
The L 42 and L 43 were developed by Schneider. These were also cylindrical in shape, had a diameter of 45 mm, a length 350 mm and weighted about 0,6 kg.
Both on the 17th of December 1944 and the 31st of December 1944, firing test were done at Kummersdorf by the Ballistic and Ammunition department of the Heeres-Waffenamtes.
The first test of the 17th of december 1944 was done to check if the firing with a sound suppressor lead to the same result as firing the mp40 without sound suppressor. The result was that the L 43 (which had an opening of 11 millimeter) did not show any difference. The L41 however only produced mis-firings. The problem was that the opening was too narrow.
The second test of the 31st of December 1944 came to a more disturbing conclusion. The L 41 was adjusted to an 11 millimeter opening. This was the new version. Now the results were similar to firing a mp40 without sound suppressor. The problem was the connection to the muzzle. The thread on the end of the MP40 muzzle was originally designed for a blank firing adaptor (which was never used by the way) which was a smaller and lighter weight device. A larger and longer device like a sound suppressor would necessitate having a longer thread contact surface (than that provided with the muzzle threads at the end of the MP40 barrel) to provide to fully functional, robust and safe mounting of a suppressor. Failing to provide for a larger thread area for mounting the suppressor would lead to mis-alignment of the suppressor and then when the bullet would leave the muzzle it would hit the baffles and destroy the suppressor and possibly insure the shooter or those around him from the suppressor being blown apart.
In addition, both suppressor designs had to use special ammunition, the so called "Nähpatrone". This ammo had heavier bullet (9 grams against the standard 8 gram) and a reduced muzzle velocity (below 320 m/s, which was standard) in order to avoid the supersonic crack which would be anything (a bullet) traveling faster than 1080 feet per second.
It's difficult to imagine that these sounds suppressors would really "suppress" all sound. A more logical conclusion is that they were used to muffle the sound sufficiently to confuse the enemy, so that the shooter could not be localized. Though keep in mind, that the British SAS and the U.S. OSS had developed relatively successful suppressor designs that had already fallen into German hands when they were captured from partisans or commandos so supplied. (Note the Suppressed STEN)