Get ya some phone books! I gather enough up to stack in a box with a 20" min length. just before leaving to go shoot I place them in a cooler and fill it up with water. Usually set two inches of book(s) in a cardboard box first, then I place a 3/4" piece of plywood and then the rest of the phone books into the box.. Like the plywood as it is sotra like hitting bone then continues through the books. The books will catch the bullet... You can also use reduced loads to get an idea how bullet will perform at lower velocitys(farther distance).
The 260rem and 6.5-284 usually penetrate close to 16 inches at 100yds. I'm into testing ammo for my 260 and -06 right now. But this summer I plan to test bullets for the muzzy.