OK, a little how-to on how we make our 4 foot diameter round targets for competition shooting. It's going to be quick and simple, but you'll get the idea.
What you'll need:
1) 1/8" x 48" x 100' Pool Wall Foam (we get ours from Amazon.com for about $60) You'll need about one and a half of these
2) Foam Pool Noodle
3) Power Grab
4) 1/8" x 24" Brass Rods (8 of them)
5) 1 can of expanding spray foam
OK, so take the roll of pool wall foam, and mark it off in 6" increments. Use a bread knife and cut the roll into 8 discs. A 100' x 48" roll will yield 8 of these, but you'll need 11 to 12 to make a full 48" target. One roll of pool wall foam will yield about a 36" diameter target.
Do the same for the pool noodle, but you'll only need one 6" section of that.
Once the pool noodle is cut, use the power grab to glue the poole wall foam to it and start wrapping. Every turn or so, squirt a little power grab on it to ensure that the foam will not unravel or loosen when it dries.
When you get the target to your desired diameter, lubricate the brass rods with some dish washing liquid, and drive 8 of them in like spokes. This will keep the layers of foam from shifting, and make everything permanent.
Once that's been done, squirt a little expanding foam in the hole of the pool noodle and you're done.
All that's left is to sew a cheapo bedsheet around the foam and paint on your bullseye!