ormandj,
yes, .260R works fine in long-throat form with 140s seated out at around 3" COAL. Nowadays most people are going the other way seeing it as a short-action cartridge and using relatively short throating for 120-130gn max bullet weight.
Top Scottish gunsmith Callum Ferguson (Precision Rifle Services) is a great fan of short-throated .260R using magazine Lawton actions and similar. Throating is designed around varmint bullets, but which also accepts the 95gn Nosler Partition. Callum says the Partition will take any European deer species going including large red deer stags. That may or may not provide the basis for your lightweight hunting rifle.
For a long-range, long-action rifle, I'd look at the 6.5X55mm first which happily gives 140s 2,900-2,950 fps MV from a 30" barrel. People do get a true 3,000 out of the standard Swede in a modern action, but that's pushing the design.
The Ackley Improved version gives the 6.5X55mm quite a bit of extra capacity because of the parent case's considerable body taper. I considered this version closely when I had a 6.5X55 target rifle built recently but rejected it in favour of the standard version because of the apparent lack of off the shelf dies. However, I've since learned CH4D lists dies as a standard number at 80 odd $US - if I'd have known then, I'd have gone AI.
http://www.ch4d.com/
The 6.5X55AI is considered by some as an ideal long-range 6.5 as it approaches 6.5-284 performance but with near 100% powder fill-ratios.
After that, it's 6.5-284 and wildcat versions of the short magnums. Performance goes up a bit and barrel life down a lot!
Brass-wise, as noted you've got good Lapua 6.5X55mm brass here now and .260R on its way. If I were building a custom .260 now I'd wait until the Lapua stuff appears to see if it's as good as other recent Lapua introductions - .22-250R, .308W Palma, and 6.5X47L which are all very high grade and also see what the neck thickness is to adopt a no-turn chamber based on 0.0015" clearance (total of 0.003")
Going in the other direction, 6.5X47L and 6.5 Hornady Creedmoor will match .260R and almost match 6.5X55mm in short actions MV-wise with 140s when suitably throated. The Hornady brass reputedly doesn't last any time at these loadings. The Lapua case suffers IMO from its small rifle primer that needs a custom action or the firing pin turned down and bolt body bushed in more mundane actions (like my FN SPR / Win M70 which has been disastrous in 6.5X47L and is being rechambered to .260R with its large primer). Anyway, why take a small case and load it at 65,000 psi when a larger one will do it with a bit more powder but lower pressures and better case and barrel life?
Laurie,
York, England
