It would seem to be a Russian Naval A3-PYa-73 (А3-ПЯ-73) practice projectile. So either drawing number 3-947 or 3-051655.
It would be used, as part of the A3-UPYaB-73 (А3-УПЯБ-73) practice round, with the 45 mm 21-K (21-KM, 21-KM-2M, etc.) series of 68 calibre guns.
The truncated forms of the projectile and round designation, as would been seen on their markings, are respectively PYa-73 (ПЯ-73) and UPYaB-73 (УПЯБ-73).
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