Hey folks!! My 2 cents:
When Jim Carmichael designed the 6.5mm cartridge which Remington adopted as the .260 Rem he based it on three conceptual premises. To load it differently than that certainly is possible within SAAMI specs but violates the targeted levels of velocity/ recoil, and his other two bases (it's been waaay too long since reading the article in Outdoor Life).
The 6.5 CM was designed for accuracy at a much higher CUP spec than the .260. To say that they are (external) ballistic twins may be close to correct. Their internal ballistics are quite not the same. Too, the chamber specifications, particularly in the throat, speak volumes as to the intended bullet weights the CM will handle in contrast to the Remington round.
Now, the point that absolutely tips the scale to the middle in favor of them both!! A man told me almost 20 years ago, regarding my two 6.5 Swedes, that relaoding the 120 pill was neither fish nor fowl in terms of a varmint or a game weight. For weeks I wrestled with that comment until it dawned on me he meant that bullet is a 'do it all' weight.
So, if you can get good accuracy from the CM chamber with fly-weights despite its longer throat, well, bully for you! Just don't expect it. The .260 may be better suited to the lighter bullets depending on how the mfr cut the chamber. And both casings have what it takes to drive 140s clean through big, tough animals.
The scales of ballistic justice will usually tip toward the middle since every single cartridge has more good than another cartridge but also carries into the comparison equally bad characteristics, be that recoil, price per box, availability in your area, harshness on barrel life, lack of punch down range, etc. (ie: a .300 magnum is better than a .243, or vice versa, the .243 is better than the .300)
So there you have it, tongue planted firmly in cheek, the definitive comment on why to avoid a difficult choice and just buy one of each!!
Exactly....
