Directional sputtering of Al and AlN on (1 0 - 1 0) sapphire was used to obtain metal-polar (1 0 - 1 3) templates. After overgrowth with AlN and GaN using metal-organic vapor phase epitaxy, we obtained untwinned (1 0 - 1 3) GaN layers. Full width at half maximum of the X-ray rocking curve of symmetric (1 0 - 1 3) GaN is less than 550 arcsec along both [3 0 - 3 - 2](GaN) and [1 - 2 1 0](GaN) directions. Ga-polarity of the layers was confirmed by high-resolution scanning transmission electron microscopy. Careful optimization of time and temperature of the initial Al sputtered layer was a key parameter to achieve high quality GaN templates.