This makeshift 14.5mm “sniper” rifle was made on the basis of 2Kh35 (Cyrillic 2Х35) insertable unified self-loading gun (or gun barrel insert) — a device which makes possible the use of small caliber ammunition for tank crews training. I’m not sure gunsmiths of which side of conflict created this contraption.
The 2Kh35 gun, erratically designated as 2X35, on the manufacturer’s site: http://www.zid.ru/eng/products/47/detail/238
