Re: zeroing a rifle
Dumb question but if the longest range you have access to is 50 then why do you NEED to zero for 100? That just means that every time you go to your regular range you will be holding under or at least dialing.
That said, you should be able to find a balistics chart from your particular ammo manufacturer that starts at 50 yards to see what the POI difference is between 50 and 100. Keep in mind that it probably will not exactly match your rifle so the only way to really know is to shoot it out of your rifle.
Being that you are in law enforcement I would think there would be a range available to you. Perhaps they will let you zero and get your dope at that police/urban hide course you are attending in Sept.