Buy some more broad heads which you plan to hunt with and practice with one of them to make sure your xbow is sited in. After finding your spot get a tape measure(rangefinder if you can$) and mark off tree with a different colored string, ribbons or bright eyes at 20 and 30 yds around your perimeter so you know the distances. Also cut some shooting lanes where you expect to shoot. Good luck but remember the thrill is in the hunt and spending time with you kids, but it sounds like you have that handled. ps 40 yds isn't that un reasonable as long as you know your limitations. Ps. a steady rest will help be it store bought or just a long version of a slingshot. Ps. Stop and visit the crossbow forum on this site.