I like taking 20oz. drink bottles, filling them up w/ water and freezing them. Those work great for up to 200m. 2 liter bottles for 200 - 400m, and milk jugs for 400m+. Good way to "recycle" your trash, or at least get one more use out of it before it goes to the recycling plant (and no, I never leave one single shred of trash at my personal range - the only range we had here was shut down by liberal bone-heads because one group of ignorant a-holes couldn't clean up after themselves ).
You don't have to freeze the jugs, the water works well for a nice effect too, but the ice is harder, and the bullet actually reacts to it more, and the explosion is more violent.
Other than that, there's an old barn in my field, with a wealth of old cinder blocks, those are nice, as well as bricks, and I even have an old Chevy small-block V8 that I have set up at 300m to test high-powered rifle penetration (the 5.56 just "chips" at it LOL, although a 70gr. Barnes did break a piece off the lifter valley out once... ) I had 2 of them, but my other one was shot with my friend's Armalite AR30 .338 Lapua... the words "obliterate" and "decimate" come to mind, but needless to say, it shattered.
"A government big enough to give you what you want, is strong enough to take what you have." -T. Jefferson