Smoothbore.75

I’m building a .308 AR10, and I’m torn between barrel lengths, I’ll mainly use this rifle for hunting, inside of 500. I think 500-800 is furthest I’ll target shoot, may try for 1000 but not very often as the closest range with that distance is an hour away, what do y’all recomend? I’m use to carrying an M1 Garand in the woods, so a 20” barrel really doesn’t make any difference to me