Shooting center fire rifles at steel at 50 yds is a big part of the problem, no matter the steel quality, shooting FMJs only adds to the problem. Steel with a center fire rifle inside of 100 is iffy to dangerous, and prohibited under the rules at any number of ranges and in the rules for several shooting competitions. I've been to ranges that limited it to 200 yds. I haven't played the game in a long time but I seem to recall that USPSA/IPSC is 15yds for pistols and 100 for steel.
As to your case, the spinner is probably deflecting the round up, then it's hitting the backstop going up and coming back. I've had the same thing happen in an indoor range a million yrs ago when I shot IPSC. I was practicing position changes, when I went prone shooting up at an IPSC target from the floor I found some of my 45 semi-wadcutters back by the firing line when I cleaned up.