My FN SPR shoots well with pretty much everything.
Choose the bullet that will meet your needs and grab any of the common powders.
I've used a ton of IMR4064 in mine, because I had a few 8lb kegs of it.
I've shot 0.5moa groups with 155gr palmas, 168gr Amax/Zmax, 168gr TMK, 185gr Juggernauts, 190gr SMK.
I've almost exhausted my supply of all the 168gr's that I had, but I have a fantastic load for the 155gr Palmas and I bought about 2000 of them really cheap a few years back....so that's what will fill the range bag for the next couple of years.
I'm using a load book recommended charge of RL15 with the 155's.
I don't get hung up on trying to find a super tiny group with the .308win.....I use it for positional practice and for recoil control practice.
Regards,
Ross