7 . 62×53mmR The 7 . 62×53mmR ( also known as the 7 . 62×53R Finnish ) rifle cartridge is a Finnish design based on the Russian 7 . 62×54mmR round dating back to 1891 . History . After gaining its independence in 1917 and after the Finnish Civil War of 1918 , large numbers of Model 1891 Mosin – Nagant rifles were in the hands of the Finnish military . As the old barrels were worn out , they were replaced by new 7 . 83 mm ( . 308 in ) barrels and the leftover 7 . 62×54mmR cartridges being in short supply , a domestic product was needed . This gave birth to the 7 . 62×53mmR . In the late 1930s the Finnish Army started loading military cartridges with domestically produced 7 . 87 mm ( . 310 in ) diameter D166 bullets as the production of new M39 " Ukko - Pekka " rifle s barreled for 7 . 62×54R diameter bullets started . This change was due in part to allow the use of captured Soviet ammunition and machine gun ammunition which often was of a slightly greater bore diameter than its Finnish counterparts . The rifling twist rate was also changed from 300 mm ( 1 in 11 . 81 in ) to 254 mm ( 1 in 10 in ) . The 7 . 62×53mmR cartridge remains in military use to this day , although it is now only used by the 7 . 62 TKIV 85 sniper rifle . PKM machine guns and other Russian weapons in use by the Finnish Defence Forces use the 7 . 62×54mmR exclusively . The Finnish Defence Forces issued instructions that when ever possible , personnel issued with a rifle chambered for 7 . 62×53mmR ( effectively the TKIV 85 rifle ) should use 7 . 62×53mmR ammunition only , and that use of 7 . 62×54mmR is only allowed when 7 . 62×53mmR is not available . Cartridge dimensions . The 7 . 62×53mmR has 4 . 16 ml ( 64 grains ) HO cartridge case capacity . The exterior shape of the case was designed to promote reliable case feeding and extraction in bolt action rifles and machine gun s alike , under extreme conditions . 7 . 62×53mmR maximum C . I . P . cartridge dimensions . All sizes in millimeters ( mm ) . Americans would define the shoulder angle at alpha / 2 ≈ 18 . 5 degrees . The common rifling twist rate for this cartridge is 300 mm ( 1 in 11 . 81 in ) , 4 grooves , Ø lands = 7 . 59 mm , Ø grooves = 7 . 83 mm , land width = 4 . 20 mm and the primer type is Berdan or very rarely large rifle . According to the official C . I . P . ( Commission Internationale Permanente pour l ' Epreuve des Armes à Feu Portatives ) guidelines the 7 . 62 × 53 R case can handle up to 390 MPa ( 56 , 564 psi ) piezo pressure . In C . I . P . regulated countries every rifle cartridge combo has to be proofed at 125 % of this maximum C . I . P . pressure to certify for sale to consumers . Differences between 7 . 62×53mmR ( Finland ) and 7 . 62×54mmR ( Russia ) . The 7 . 62×53mmR is practically interchangeable with the 7 . 62×54mmR , the 54R will fit into the smallest allowed chamber size for the 53R , but is nevertheless a different cartridge made to different C . I . P . standards . Using military steel - jacketed 54R Russian ammunition in weapons made for 53R is not recommended ( except the M39 and 7 . 62 TKIV 85 rifles designed to allow safe use of 54R in case of emergency ) , as it may rapidly wear out the barrel . Even worse , there is a possibility that the resulting pressure from the steel - jacketed larger diameter bullet is too much and firing it may result in severe damage to both the rifle and the shooter . Using the 53R in a gun made for the 54R is however safe , although it may result in accuracy well below the weapon ' s potential . The Finnish commercial ammunition manufacturer Lapua does not make a difference between the 53R and 54R , but produces cartridges that will function in weapons chambered for either one . The Russian ammunition maker Barnaul states that Russian cartridges marked 7 . 62×53 are the same as 7 . 62×54 . From their web site : " Some hunters have been confused because there have been varying marking on the package , case bottom and stamps : 7 . 62×53 : 7 . 62×53R : 7 . 62×54 : 7 . 52×54R . This happened because the 53 . 72 mm case length was rounded off differently in various countries . After Russia became a member of the European Permanent Coordinated Commission , the final name - " 7 . 62×54R " - of the cartridge was accepted . " Additionally , Russian ammunition manufacturer LVE ( Novosibirsk Cartridge Plant ) states , " The cartridges cal . 7 , 62×54R are produced by various producers around the world . Producers mark these cartridges differently , and this leads to confusion among the customers – 7 . 62х53 ; 7 . 62×53R ; 7 . 62х54 ; 7 . 62×54R . The confusion is based on difference in rounding out ( rounding up or rounding down ) the case length ( case length of our cartridges is 53 . 65 - 0 . 2 mm ) . The letter " R " indicates a case rim . After Russia ’ s joining European Commission ( ПМК ) a definite name of this cartridge was determined – 7 , 62×54R . Therefore you may use cartridges of caliber 7 . 62х54R freely with your arms [ marked as 7 . 62×53R ] . "