Whoa! Many excellent responses. I wouldn't have thought 6.5mm/.264 was that popular. Thank you all.
CrackerJack: I hear you on the diminishing returns with mags, but I am looking for another long range setup (I have a .308 setup I'm quite happy with.) I'm a single dad, and my older son wants to start shooting seriously with me. .260 or 6.5x55 Swede would be nice for him, but he can handle the .308 too. Long range target shooting (and potentially pronghorn hunting, but more likely mule deer) would be the intended use, with the emphasis on target shooting. My idea of fun is shooting pop cans (or attempting to) at random distances 300-700+ yards out. Random distances, estimate range, estimate wind/drop, etc. I do expect to move back to Albquerque though, and I've always wanted to hunt pronghorn, which are hard to get up close on. 6.5 was chosen because of the BC/ballistics, and long range is attractive to me in a smokeless centerfire rifle. Thanks very much for mentioning 6.5/284. I was browsing Speer when I got the bug for this, but did find 6.5x284 in my Hornady reloading manuals. (Reloading is a large percentage of the fun for me.)
JohnKSa: Considering the similarity of .260 and 6.5x55 Swede, I think your point that there is no advantage to the .260 is well taken. I'd choose the Swede (which I do find very interesting). I'm thinking a short action is probably out, and I'd go with a long action to have more room to play with OAL, rather than have issues with magazine-imposed OAL limits. Thanks also for mentioning 6.5-06, which sounds very attractive. I found that in Hornday, and it seems to have the edge on everything but .264 Win Mag, and isn't belted. Forming cases might require neck turning though....
I'm curious why the popular (and neglected in my thinking) 6.5/284 is being considered for long range shooting over the 6.5-06 or .264 Win Mag. It seems these would have an edge.
GunBlast: I know next to nothing about the Grendel. This is a potential AR round, no? Considering this to be a long range bolt gun, should I explore this further over some of the cartridges listed?
Drue: I've heard the .264 Win Mag barrel-life point. At this point, being compelled to tinker and inspired to dream, an eventual rebarrel wouldn't be an issue, I'd consider it a sign this was a successful project! What bothers me more is the concept of reloading a cartridge that headspaces off a belt instead of the shoulder. (Maybe I just have to get over that though.)
mete: You're right on what attracted me to this caliber. Perhaps you have insight into why 6.5/284 is becoming the attractive cartridge over .264 Win Mag or 6.5-06. Efficiency?
USSR: Your post let me know that 6.5x55 wouldn't fly in a short action, which I didn't realize (sounded .308 Win size to me). Thanks. Hmmm...1000 yard F Class...damn...that sounds fun! I'd like to seriously try that, after practicing, and watching an event to see how embarassed I might be! (I remember reading a story of a 1999 competition in England where the winner, who shot a 6.5x55 Swede (sako/tikka?) put _10_ rounds in 4.5 inches at 1000 yards
...and I thought TGO was impressive with a pistol! Damn!)
atblis: I hear you on action length! I've also considered/reconsidered wether I really want a Mauser action. I was looking at Sarco Inc. for Mauser actions, and was a bit disappointed in the surplus stuff. (Conditions offered, no VZ-24 actions, no good German 98K actions, and I believe the K31s were small rings, but could be wrong.) I'm also wondering if I should consider a stiffer Rem700 action with a faster lock time might be appropriate for long range shooting. It seems like a Mauser or Savage action would be easier to rebarrel. I need to get the Kuhnhausen mauser manual and learn more before part selection. Never tried Rem brass. I've had good results in .308 with everything I've tried though (Win, LC, Norma, and Lapua...I'm probably the only one not to see an accuracy difference, but I'll be damned if Lapua isn't ready to load out of the box. A bag of Win requires some work, but shoots well for me. The only thing I don't like about LC is the fact that I have to work up seperate loads with it. I need to standardize for this project on just one. Probably just a few hundred Lapua to start, depending on the cartridge chosen, availability, and the need, if any, to form original cases.)
Ol' Joe: Heh, another vote for 6.5x284. Other than barrel life and efficiency, is there a compelling reason? Wouldn't 6.5-06 or .264 Win Mag have an edge in the wind?
Michael_aos: I expect I'll be going for a 10-11lb rifle here too. 26". I would like a 6mm BR too (theres a cartride I'd hate to get stuck in a die though!)...but I have a never ending yen for guns...and sons to send to school. This splurge should keep me going for a few years, I expect to feel really guilty after I buy a suitable LR scope. But life's short!
Preacherman: I hear the call of the Swede too. Very likely if this evolves into my sons LR gun. (He did make honor roll the last 6 quarters in HS). The only thing is that legend and history are reflected in most of my guns (the majority are BP, several flinters, 1911s, BHPs, Colt Walker (clones) etc.). The goal for this is a long range shooter.....but I'd have likely said the same thing to an anonymous poster!
Thanks all, for the help with this project. Much thinking to do. I do believe that I've ruled out .260 Rem and 6.5x55 Rem Mag. Many good choices left: 6.5x55 Swede, .264 Win Mag, 6.5-06, 6.5/284.
Much thinking to do!