I currently use a 100 yard zero for my patrol rifle. Other officers use the 50 yard zero. I suggest that you read the following article as the author explains the system better than I ever could. Please try:
Long Gun Zero – Law Officer
After you read the article, if you decide to use either the 50 yard or the 100 yard zero, then use the following link to print out a sight-in target.
100 Yard Zero Target - Documents
This system has worked for me, fellow officers, and operators on our weapons team. I hope that it works for you.
Good luck.
Joe