The way you set up the drywall will make a difference, as noted above.
Several sheets glued together will give you a different penetration depth than several sheets separated by three inches of air.
Same if that air space is filled with insulation.
Your glued-together test might be fun, but it won't tell you anything useful in applying it to house construction and penetration.
How many sheetrock sheets would it take to stop a recoverable bullet?
I built a dummy section of "wall" using leftover drywall from construction in my house a while back.
Frame of 2x4, drywall on both sides.
I was testing RUBBER buckshot.
ALL pellets from one less-lethal 12-gauge shell penetrated BOTH drywall panels from about 15 feet away.
I didn't include insulation because I didn't have any to spare laying around.
That may help give you an idea.