How I remember is anything based on a 30-06 cartridge is a long action---.270, 25-06, .280, etc. etc. etc. Basically, the full sized cartridges.
Anything based on a .308 cartridge is a short action, .308, 7mm-08, .260, etc. and then also the .223, .222, 22-250, etc.
If it's a "short" cartridge, it's a short action, and if it's a long cartridge, it's a long action. I don't know where the cut-off is, but that's how I generally remember it. I'm not an expert however.