<Tr> <Th> Muzzle velocity </Th> <Td> 777 m / s (2,550 ft / s) </Td> <Td> 640 m / s (2,100 ft / s) </Td> <Td> 716 m / s (2,350 ft / s) </Td> <Td> 747 m / s (2,450 ft / s) </Td> <Td> 930 m / s (3,100 ft / s) </Td> </Tr> <Tr> <Th> Muzzle energy </Th> <Td> 550 J (130 cal) </Td> <Td> 530 J (130 cal) </Td> <Td> 665 J (159 cal) </Td> <Td> 650 J (160 cal) </Td> <Td> 785 J (188 cal) </Td> </Tr> <P> The P90 uses a unique horizontally mounted feeding system--patented in the United States--that contributes to the weapon's compact profile and unusual appearance . U.S. Patent 4,905,394 ("Top mounted longitudinal magazine") was awarded in 1990, naming René Predazzer as the sole inventor . The detachable box magazine is mounted parallel to the P90's barrel, fitting flush with the top of the weapon's frame, and it contains 50 rounds of ammunition which lie in two rows facing left, offset 90 ° from the bore axis . As the cartridges are pushed back by spring pressure and arrive at the rear end of the magazine, they are fed as a single row into a spiral feed ramp and rotated 90 degrees, aligning them with the chamber . The magazine body is composed of polymer, and it is semi-transparent to allow the shooter to see the amount of ammunition remaining at any time . </P> <P> The P90 was originally equipped with the Ring Sights HC - 14 - 62 reflex sight, but the current weapon is instead fitted with the Ring Sights MC - 10 - 80 sight, which was specifically designed for it . The HC - 14 - 62 has a polymer housing and uses a forward - aimed fiber optic collector to illuminate the white daytime reticle, which consists of a large circle of about 180 minutes of arc (MOA), with a 20 MOA circle surrounding a 3.5 MOA dot in the center . The MC - 10 - 80 has an anodized aluminium housing, and has a similar black reticle . The night reticle for both the HC - 14 - 62 and the MC - 10 - 80 consists of an open T that is primarily illuminated by a tritium module, and, in the HC - 14 - 62, ambient light drawn in by an upward - facing collector . The sight is adjustable for both windage and elevation, and it can be used in conjunction with night vision equipment . As backup in case the reflex sight is damaged, a set of fixed iron sights is provided on each side of the reflex sight housing . </P>

How does the magazine on a p90 work
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