Thread: Gongs

Just read moosemans thread on gongs from mucko. A few of us out in the sticks are interested in stretching the legs out to 1000 yards on a property one of us owns.
We have some biz 80, and ar 500 already that fit the bill to 400. Rifles run through 300 win mag, 7 mm wsm, 280 rem, 308 and my springfield.
The question is what thickness is best for the new targets to avoid them getting damaged.
Brother in law works for steel and tube so hope to get it at reasonable cost in palmy