The .260 Remington and 6.5 Creedmoor are incredibly similar rounds. Both use the streamlined 6.5mm bullet diameter and both are typically directly compatible with .308 Winchester rifles with a barrel switch. While the .260 Remington was and still is well-known in hunting circles, the 6.5 Creedmoor has been the recent star of the precision rifle crowd.
Sniper’s Hide, an accomplished shooter himself, takes a look at the two cartridges and their intended usages. In short, the 6.5 Creedmoor is a great choice for new shooters or those who do not reload, while the .260 Remington is a better round for those who have experience with reloading.
With its commercial acceptance, the 6.5 Creedmoor is simply easier to find. Compared to the .260 Remington, the typical cost of match ammunition is 50% less. While easily reloadable, the Creedmoor is typically considered to have “softer” brass which will not last as long, or have as high of performance.
In favor for the .260 Remington is base velocity (one can typically squeeze about 50 fps over the Creedmoor) and the brass, which Sniper’s Hide makes a point is from either Hornady or Lapua. Further, the .260 Remington “loaded to the lands” may be a bit too long for the standard AICS magazines.
Sniper’s Hide goes into further detail on his own article available here. Check it out and learn from an accomplished long-range shooter.