Re: Custom Rifle - 500 yards max - what cartridge
Lots of good options out there but I would personally be looking at something in 6.5 for the purpose you mentioned. The 260, 6.5x47, and 6.5x55 would be at the top of my list. They offer everything you are looking for. Yes, the 308 is going to get more barrel life but the above mentioned are no slouches in this regard. I would put barrel life at the bottom of the priority list anyway since all the cartridges we are talking about are going to be more than sufficient and terminal performance would be at the top of my list.
Very Low recoil
Very good SD
Very popular so lots of factory ammo if needed and lots of great bullet options
Lots of great 6.5's to consider.