I use 47.4IMR 4350 w/139Lapuas, and in 28" barrel this provides 3025fps.
I calculate accurate barrel life with this load at ~1800 with 1min/shot.
I recently swapped a barrel at a shot count of 743, and I measured .006" of leade movement on it.
This is better barrel life than would be seen with a 6.5-284, but this cartridge could not possibly match 6.5-284 potential. Any implication to the contrary is flawed.
I think the 6.5WSSM represents the perfect capacity for 26cal.
Winchester's reloading 25wssm brass is very very good.
Two things to consider though:
1. WSM brass is the parent of WSSM brass. They just formed it down.
This makes it extremely thick, because WSM body thickness becomes WSSM neck thickness(~20thou). So don't even consider the WSSM for any accurate use without a plan to turn the necks. And turning necks so thick is not easy.
2. The WSSM is at magnum cartridge diameter, so you need a magnum action.
This ensures enough barrel steel around the chamber, allowing proper extraction with typical to stiff loads. The WSM/WSSM actions generally use larger diameter barrel threading.
The 6.5WSSM would be matched with a 260AI. But good 260 brass? Does it exist?
A 6.5-284 could be formed down just as the WSM was, to match the WSSM capacity. But Winchester has already done that for us.
