I shoot at an indoor range where targets are held by overhead trolleys. Thus, I don't need refrigerator cartons as target backers. Any old 12"x12" piece of cardboard will do. I tape the cardboard securely to the paper target. It greatly reduces the tearing of the paper and leaves cleaner holes so I can get more shots into a given target. That's especially important for a shooter like me who groups so many shots into the bullseye.
I also use the same Birchwood-Casey target every time. That way, I have a consistent basis for comparing accuracy across many range sessions. I have years of data from each of my guns from these targets. As an accuracy score, I calculate the percentage of my shots that hit within a 4"x4" square around the bullseye.
Below is one of my better targets (did you think I'd put up a lousy one?

), from my Shield 45 @ 15 yards, standing, two-hand. I was shooting American Eagle FMJ 230g. Note that the holes are much cleaner than what you'd typically get from round-nosed .45 acp with an unbacked target.