Hello
I`ve tried using the accu copper coated lead bb`s and there also slightly larger,and in several of my bb pistols,the pistol stops as if the mag is empty but isnt! especially with the ppks and the 1911 bb pistols,i use umarex or h&k steel bbs.
Carpet/carpet tiles are the best for stopping a bounce back,or if you were to use the copper bbs a steel pellet catcher should deform them enough to stop them coming back!!
Hope this makes sense and helps..