I have found that the "pumkin balls" were ok in my 835. However I had best results with sabot slugs. Hornady sst and Federal premium Barnes expander shot equally well. I got 2 inch groups at 100 yds. I have a scope so this info will not directly correlate to your setup. I sight in dead on at 100, about 4" low at 150. The ballistic calc says zero at 150, not more than 3" over at 100 and 6" low at 200. I prefer less variance from line of sight. Killed a deer at 125 yds w/ the sst last year, head shot a coyote at 40 yds this year w/barnes. Let the barrel cool for 5 minutes between shots after 2. The barrel heats up fast and groups get really big, really fast.
You can't fix stupid....however ignorance can be cured through education!