another way is to shoot through two targets at once with an offset between them that corresponds to the difference in impact points at 6 and 10 mtre ranges. The front "target" could be just a photocopied "aiming mark" with a guideline on it corresponding to the required offset. By doing this the rearmost target would be the "scoring one" but the holes might be a bit fuzzier than shooting through one card only (just realised already suggested by previous poster).

Vic Thompson.