Do you really think an animal will know the difference between these two? I'm thinking if I needed more zip from a 6.5 bullet, why not just build a 6.5-06, 6.5-06AI, or go with the 6.5 win mag?
I seriously doubt the 6.5x55 kicks a 260's ass. That's a stretch, but, are they both fine cartridges, absolutely.
