The 260.rem cartridge is a short action cartridge based on the .308 winchester.
Short. Compare cartridge overall length to a .308 Winchester. That is a short action. Longer than that is a long action.
Long action. .308 and shorter- short action. 30-06 and longer, long action.
Long action. The .270 cartridge was based on the 30-06, a long action. .308 length is short action.
30-06 and longer cartridges are long action. .308 is short action.