Primos tightwad .570 or Remington super full .572 i 've shot the 18.5", 21",and the 26" barrels on my 870 and that .570 range just seems to throw a very forgiving pattern while still keeping around 280-300 in the 10. The two longer barrels were really not that picky about chokes and tss doesn't need an $80 choke to pattern well. High numbers .555-.562. Forgiving .570-.585