With a long action I would go with the 6.5 x 55, you can get Lapua brass for it and for me that makes the decision right. The last reamer I bought was a 6.5 x 55 AI and it shoots 139 g Scenars with great accuracy, I cleaned some 20 round relay targets at 300 meter when I was fire forming new brass.
I went with the AI to compete with the 6.5 x 284 as I have the same volume and maybe I will get longer barrel life. The 6.5 x 55 will easily get you to 1,000 yards especially with handloads, the factory loads are anemic so some of the older Norwegian Krags do not blow up.
Think about how many cartridges are still going strong after 100 years, they must have done something right in the design.
My 2 cents,
wade
I went with the AI to compete with the 6.5 x 284 as I have the same volume and maybe I will get longer barrel life. The 6.5 x 55 will easily get you to 1,000 yards especially with handloads, the factory loads are anemic so some of the older Norwegian Krags do not blow up.
Think about how many cartridges are still going strong after 100 years, they must have done something right in the design.
My 2 cents,
wade