juan , I have a benelli nova 20 like yours and have found that it will throw a killing pattern at 30 with winchester supreme or turkey thug 5's but not any further with any lead I have tried . I run a $20 tight wad choke in mine also from walmart . To get to 40 yds with a killing pattern you will probably find you need to shoot Federal Heavy weights in 7's . They run around 20 to 25$ for 5 shells but will kill with authority at 40 yds. They will also shoot very well in your sons gun also with the choke he already has . Also if you buy some try them in your factory full choke , a lot of people have found they perform very well in factory chokes .