I built a water test .
It is a trouth 1' wide and 1" high
I used plywood for the sides , bottem and far end
It is 4' long
I use cardboard for the end I shoot through
It is filled with 1 gallon plastic bags filled with water seperated by a piece of cardboard.
The cardboard is to tell just how far the bullet penatrated ( some times the shock brakes bags not hit )
I sit this on saw horses at 100 yd or any other range that I can hit the center of the the target.
I hit it last year with a 375 HH and got full penatration with solids ,so be carful of the back stop
If not centered or if the bullet mushrooms funny it comes out the sides or top some times.
It makes a mess with all the water flying