RNS points out a brilliant idea: using pool cue chalk as a reactive target:
Billiards chalk is 7/8 of an inch per side and even when hit with something as slow moving as a standard velocity 22LR out of a pistol, makes a bigger poof than Charles Nelson Riley.
If you can hit it.
I found cheap chalk ($12.95 for 144 pieces) on Amazon and just placed an order.
And then there’s this:
Some of the people at the range will tell you that you won’t be able to hit them. Some of them will actually get amusement from telling you so repeatedly. Even when you hit your first one, they’ll call it luck. After you start hitting them in strings, those same people will then tell you about how they could probably do that with an SKS.