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  1. #21
    Join Date
    31.07.2002
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    UK
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    183

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    Quote Originally Posted by fert View Post
    Tony, I think you already received a text about Scotti guns from the Cesim. I wrote it
    regards
    Hi Fert, sorry to bother you about this, but could you send me the text direct please? I have tried contacting AZ with no luck.

    My email address is williams(@)quarryhs.co.uk.

    Thanks for any help,
    Military gun and ammunition website: http://www.quarryhs.co.uk

  2. #22
    Join Date
    31.07.2002
    Location
    UK
    Posts
    183

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    OK, I have put together the information I have to date concerning the experimental Scotti 20 mm guns and ammunition, as follows:

    Alfredo Scotti, who established the Società Anonima Armi Automatiche Scotti (Armiscotti) in Brescia near Milan, designed a delayed blowback action which he considered to be suitable for automatic weapons of all calibres. The gun fired from a locked breech which was then unlocked by means of a gas-piston system; locking was by means of a rotating bolt head; extraction was powered by blowback. The lack of primary extraction required the cases to be lubricated.

    Several different models of Scotti 20 mm gun were designed and built, but only one saw service: the 20/77, which has its own entry below. This entry concerns the other guns, in so far as they are known – there are still various uncertainties.

    Scotti started work on a 20 mm gun in the late 1920s and in 1931 formed Brevetti Scotti AG, a joint company in partnership with the owner of Oerlikon, Emile George Bührle. In the following year Oerlikon acquired the patent rights to Scotti's products with the exception of Italy, for which Isotta-Fraschini held the rights. The development of Scotti's 20 mm cannon is not entirely understood, so what follows is subject to change if more authoritative sources emerge.

    In 1932, the first prototype of Scotti's 20 mm cannon appeared, designated M32 or MG 20/70, as it had a 70-calibre barrel. Three years later came the M35 or MG 20/40, a much shorter and lighter gun specifically for aircraft. The M39 or MG 20/90 came next, with a very long barrel as it was intended to be an aircraft motor cannon with the barrel reaching all the way to the propeller hub. Finally, there was the M43, a lighter (56 kg) aircraft version of the M41 AA gun.

    The ammunition used in these guns is debatable, with conflicting information from various sources. One of the few certainties is that Scotti developed his own cartridge, a 20 x 110 which was a half-way house between the Oerlikon S 20 x 110RB and the Hispano-Suiza 20 x110 of the HS 404: it combined the sloping shoulder of the Oerlikon with the rimless base of the Hispano. At least one case survives, helpfully headstamped 20 mm Scotti 1933, thereby providing a date as well as confirming the purpose. Sources generally agree that Scotti started out using Oerlikon ammunition (not surprising, given his close links with the company) with both the 20 x 110RB Type S and 20 x 99RB Type L mentioned. Possibly both were used in different prototypes, but given the relationship between the Type S round and Scotti's own cartridge, the balance of probabilities suggests that his M32 gun started development with the Type S ammunition and finished with Scotti's own cartridge.

    Brief details are provided of the M35 Scotti aircraft gun in an Oerlikon-Contraves Museum catalogue: it is stated to weigh 23 kg, with an 80 cm barrel (much smaller and lighter than his other 20 mm guns), fed by a 15-round box or 60-round drum magazine and fired at 350 rpm. The size and weight of the gun are similar to the Oerlikon FF so the ammunition was also presumably comparable to its 20 x 72RB. This ties in with a drawing from SMI (the ammunition maker Società Metallurgica Italiana) of a 20 x 70 Erhardt round dated 1936 and titled bossolo modello F per mitragliera Scotti 20mm (= model F case for Scotti 20 mm MG); it does seem surprising that the cartridge from the obsolete German Erhardt cannon was selected, but that was presumably the most suitable one available with the required performance (cases with rebated rims like the Oerlikons are not desirable in other than API blowback guns). The museum catalogue also gives an MV of 850 m/s but that cannot be right and must have related to another cannon: around 600 m/s would be in the right ballpark.

    In 1939 Scotti proposed an engine-mounted aircraft gun with a 90-calibre barrel and a belt feed. Sources are in conflict concerning the ammunition: one source states the Rheinmetall 20 x 105B, but its bigger brother (20 x 138B) seems more likely, as it was already in Italian service. However, at that time there were practically no liquid-cooled vee-engines used in the Regia Aeronautica able to take an engine cannon, so this version also remained experimental. The M43 aircraft gun almost certainly used the 20 x 138B, as it was a lightened version of an AA gun using that ammunition.

    According to Chinn (but unconfirmed), some of the Scotti aircraft guns were sold to small countries in Europe and South America, and the cannon was ultimately developed to use belt feed and to reliably achieve a RoF of 600 rpm. However, it is not clear to which models he was referring.

    It appears that Scotti's cannon provided some inspiration to Marc Birkigt of Hispano Suiza France (which had a close working relationship with Oerlikon), in the development of his HS 404 cannon, which started in 1933. This also uses a delayed-blowback gas-unlocked action (albeit with a different locking system, using pivoting flaps rather than a rotating bolt head) and the cartridge case seems to have been developed from the Scotti's, with a sharper shoulder.
    All comments welcomed!
    Military gun and ammunition website: http://www.quarryhs.co.uk

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