It is very difficult to be confident in identifying experimental Russian aircraft guns because they used (and still use) a range of different designations. It is therefore possible that two or more different designations for a given calibre of gun might be describing the same gun.
The organisation of Russian military equipment procurement has differed from the usual Western practice in that designs are produced by separate Design Bureaux (Osoboe Konstruktorskoe Buro, or OKB for short) and, once approved, are allocated to factories for production. At least two Design Bureaux were concerned with gun design at around the end of World War 2; OKB-15, led by Shpitalny, and OKB-16, originally under Taubin but later led by Nudelman and including Suranov and Rikhter. One designation used is therefore that of the Design Bureau, and two different 57mm airborne weapons have been identified from these bureaux; the OKB-15-57 and OKB-16-57.
A second form of designation honours the designer by his initials. Three different gun designations occur in texts about Russian aircraft; N-57, NS-57 and RShR-57. The questions are; are all these designations genuine and how do they relate to the OKB numbers?
There are other forms of designation used (e.g. the NS-37 was also known as the 11 P-37) but it is possible these might be concerned with particular mountings rather than the guns (this practice still exists).
There is clear evidence (from a book by Nudelman) that the N-57 and OKB-16-57 were one and the same, and that this weapon was a compact, low-velocity gun not intended for anti-tank use. An illustration exists of both the gun and ammunition together with data on the performance, and it appears to be a scaled-up N-37. As far as I can determine, it was only ever fitted to the first prototype of the MiG-9.
Data on the OKB-15-57 is included in Bill Gunston's Encyclopedia of Russian Aircraft and from this it is obvious that it was a very powerful weapon, much bigger than the N-57 and intended for anti-tank use. Gunston's text refers to an NS-57 (but does not specifically link this to the OKB-15-57 in the data table), and other authors refer to a RShR-57. It is now known that RShR referred to Rashkov, Shentsov and Rozanov, but it is not clear which design bureau they worked for. I tentatively identified the OKB-15-57 as the RShR-57 rather than the NS-57 as "NS" in other designations refers to Nudelman and Suranov, who belonged to OKB-16, so I do not believe that NS-57 and OKB-15-57 can be the same . I accordingly ignored the NS-57 designation in "Rapid Fire" because I don't know what it might have referred to; there is no mention of an NS-57 in Nudelman's book. However, it appears that the RShR 57 might have been hand-loaded, which would mean that it could not be the same as the automatic OKB-15-57 listed in Gunston's book.
Any further information on this subject (or on the totally mysterious "N-45") would be gratefully received!
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