That's what I was thinking, but I'm starting to find examples of guys resizing 7.62 LC brass to 6.5 CM. On a side note, PWS makes an MK220 (long-stroke piston AR-10) in 6.5 CM. That's my 2nd favorite AR10.
Here's an intriguing example:
http://www.65creedmoor.com/index.php?topic=1996.0
"I've been shooting the 6.5 Creedmoor for approximately 2 year. I've fired in excess of 1100 rounds between two rifles. The first rifle was a Savage 10FCP-K that I rebarreled to 6.5. A Krieger 1-8.5 barrel was used. I have since built a new rifle using a Pierce Engineering short action repeater mated to a Broughton 1-8 5C barrel that fits in a Eliseo R5 chassis system. When I started to reload for it brass was difficult to find. I began forming the 6.5 CM case from Lake City and Federal Cartridge once fired brass. It was a challenge, however, I was successful. I do not use any brass but L.C. or F.C. The brass must be hard when working it. If you anneal it before forming you will crush the brass. Anneal after the forming. I used Redding full length sizing die with the decapper removed. Imperial sizing lube was used for the lubricant.
There are advantages to using LC and FC brass. It has a thicker wall and does require neck turning. This allows a tighter neck in the chamber. I turn the necks to .295 diameter. Saami spec for the neck diameter in the chamber is.296 diameter. I trim the brass to the minimum length and have not needed to trim any so far. I only neck size using a Redding bump die. Because the brass is thicker it will take a higher pressure charge. Currently, I am using Winchester large rifle primers, 44.0 of Ramshot Hunter for Hornady 140 BTHP Match and Nosler 140CC. 44.3 grains of Ramshot Hunter for Berger 140VLD and 140Hybrid. The powder charge is not compressed. I have observered that the 140 & 142 grain bullet are concidered heavy bullets. Heavy bullets use slower burning powders. I have achieved a stable muzzle velocity of 2950 fps average with excellent accuracy. There are no pressure signs such as crateing or pierced primers. No loose primer pockets. No smileys on the head. I cannot say how long my barrels will last. There was a lot of trial and error. Emphisis on error.
Hornady picked a winner. The 6.5 Creedmoor is a fantastic cartrige and has a lot of potential. It's performance can be improved.
I retired my 308."
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Also neat:
http://txbrassworks.com/lake-city-762-creedmoor-conversion/