PTRS-41 14.5mm
In the summer of 1941, after the German attack on the USSR, the authorities asked Sergei G. Simonov to design a large-caliber rifle with antitank capability. Shortly after, the 14.5mm PTRS-41 appeared. It was very similar to the PTRD-41, although more advanced, longer and heavier than the previous one. The PTRS-41 fired the same ammunition as the PTRD-41, but instead of being a single-shot rifle, it carried a magazine (clip) with 5 bullets. The rifle had a muzzle brake and was operated by a gas-piston, which considerably reduced the enormous recoil and made it easier to fire than the PTRD-41. Also, this new system allowed them to be more accurate. The PTRS-41 was less robust and more delicate to maintain in the battlefield, and the magazine could only be introduced in a way, so it was not as appreciated as the reliable and simpler PTRD-41
PTRS-41 gallery and more info