I have shot about 10 different bullets and 5-6 powders through 2 different 26's. Plus the three different factory loads (on sale so it was 1/2 price of just buying brass).
#1- that 129 factory load sucked in both my rifles. From the nosler m48 it would do 2-3 moa groups, from my fierce best was around 1moa. Also you prob want to go to a heavier bullet anyways, that 129 is pretty explosive at closer ranges.
The nosler 140 accubond load was accurate in both my rifles. I made a duplicate for the rifle I kept, 88gr of us869 and seated .020" off the lands. Ran a couple ladders, and shot a few groups, right there was the most consistent accuracy. 3290fps from my fierce with a 26" barrel.
The barnes lrx was accurate in both rifles, in the fierce I run 79.5gr RL33 seated .070" off the lands, 3493fps and consistent 1/2moa accuracy. Thats the bullet I stick with now, pretty effective.
I would seriously think about trying one of the solid copper bullets, CED, hammers or barnes. The 26 can push a 130-140 pretty hard and the softer cup and core bullets expand pretty drastically at those speeds.