Use #6 shot, #5's and 4's are hard to get a good pattern sometimes. #6's might be an eye opener. I have a 535 with a 20" bbl and I am getting around 115 in 10" @ 40yds with winchester 3-1 7/8-#6 gray box. Make sure you are shooting a large target to see where your point of impact is. I use 3ft wide masking paper behind my targets on a sheet of osb to see where the majority of my pattern is to make adjustments if necessary. 670 factory choke works great in mine. Hope this helps.