My son and I both killed deer with our xbows using these arrows http://www.sportsmansguide.com/net/c....aspx?a=913285
and 125 gr. Grim Reapers broadheads designed for cross bows. The combo of arrow and broadhead were amazingly accurate out of both xbows that are different draw weights and from different manufacturers. The Grim Reapers come with a practice head that flies exactly like the real broadhead.
Another thing that aided accuracy from his Horton was the use of a cocking device. It puts the string in the same position every time. The human error factor is diminished considerably and it is much more consistent.