A 180 grain .308 bullet has a sectional density of 0.271
A 140 grain .264 bullet has a sectional density of 0.287
Yes, a 260 Rem has a slightly higher SD (.016 or 6%), but not enough to offset 40 grains more weight (28%) and 36% greater frontal area in the 308.
In either case, use a premium bullet.
Better yet, for higher sectional denisty are the 156 gr. NORMA bullets - heavy, premium bullets in 3 varieties (see:
http://www.norma.cc/content.asp?Typ=28&Lang=2&Submeny=4&Rubrik=Components )
Many guys in my hunting team use Norma Oryx bullets (which are bonded). I have seen many of these 156gr Oryx bullets recovered and every one of them has expanded well, penetrated quite deeply, and lost perhaps 10% of their mass -- and some of these are after hitting big moose leg bones. Same story for the Oryx bullets in .30 cal too.
Overall, I think the performance or these Norma Oryx bullets is very similar to Woodleigh bullets (and, at least here in Sweden, the cost is much less for the Oryx bullets).
Steelhead is right - a 6.5 x 55 (or a .260 Rem) loaded with these 156gr bonded Oryx bullets looks like it should scare a critter to death!
John
