Prvi Partizan cartridge cases are the best modern commercial cases any Enfield owner and reloader can buy. Prvi .303 cartridge cases have rims on average .004 thicker than any other brand which helps eliminate headspace problems. Prvi cases have a base diameter on average .004 larger than any other brand. Prvi .303 cases are also .010 thicker in the critical base web area of the case where case head separations can occur. Below are two .303 cases fired in my 1943 Maltby No.4 Enfield, you can see the difference on the effects of the larger the dimensions on the Prvi case. The much praised Greek HXP cartridge case has a much smaller base diameter and the case has expanded out to chamber dimensions. This expansion you see in the web area is where a case head separation will occur if these cases are full length resized repeatedly. The reason Prvi Partizan ammunition is less accurate in the majority of Enfield rifles is because of throat erosion from cordite powder and muzzle wear. In Enfield rifles with new barrels or having very little throat erosion they should shoot just as accurately as flat base bullets. Factory loaded Prvi .303 ammunition use a “standard” boat tail bullet design and the base of these boat tails will not obturate or expand and fill the bore when fired. This causes the bullet to slide down the initial eroded rifling without engaging the rifling and destroys accuracy. Another factor with boat tail bullets is muzzle wear which can deflect the bullet as it exits the muzzle. As you can see below cordite loaded Mk.7 ammunition had a flat base bullet and the nitrocellulose loaded Mk.8Z used a rebated boat tail bullet. Mk.8Z ammunition used a rebated boat tail bullet to improve accuracy Below are the restrictions and explanation on hotter burning cordite powder and boat tail bullets. You can purchase new Prvi Partizan cartridge cases which will last much longer when reloading, or just buy the loaded ammunition if your bore is in good condition. Prvi ammunition is loaded with a double base ball powder with a burning rate close to the old surplus Hodgdons BL-C2.