The major concern about penetration of dry wall seems to be whether a shot fired in one room could penetrate a wall and kill or wound an innocent person on the other side. So I suggest, if possible, that the range be smaller, say 30 feet (10 yards) which would be across a rather large room. Not many houses would have a place where a wall was 25 yards away.
Then you might test closer ranges, to simulate a person firing closer to the wall, maybe a 3-7 foot range.
Don't forget to tell us what thickness of drywall is used. There is a lot of difference among 3/8, 1/2, 3/4, 1 and 1 1/2 inch drywall. The first, as you know, is the most common in homes today, but 1/2" was common in the past, and a few special buildings use as thick as 1 1/2".