The place to ask is at your range, to see if that particular location has enough shotfall acreage for No 7.
NSSA rules limit shot size from 7 1/2 to 9 but for practice No 7 would be ok, IF the field is large enough.
By Journee's Formula, the maximum range of No 7 1/2 is 209 yards, for No 7, 220 yards. NRA recommends 300 yards for a safety margin in case somebody slips in something bigger.