I Love my older Caldwell Leadsled.....nice and sturdy,keeps down the recoil and helps me get my Rifles sighted in Dead On!
As several mentioned,I start out at 50 yards then out to 100 yards dead center!This is using a Scoped Rifle and I do it with pretty all my Rifles be it Smaller Predator Calibers on up to Deer specific Rifles!

With an open sight Rifle You may need to keep it closer since it's going to be difficult to see further out.....or use a larger target!