Exploding targets


My son likes to shoot exploding targets. These targets used to come fully assembled, just stick them on and shoot. He used to get them with .22 long. Several years ago there was a major marketing change by which the target must be assembled by the shooter from 2 chemicals, a hollow frame and a sticky. Ever since this change the target just falls apart instead of exploding when he hits it with .22 long. I am told that this new type of target can be defeated only by using .223 (and higher) velocity-wise ammo. Why?


Vlad, maybe the composition inside got desensitized/phlegmatized for safety reasons or to make it impossible to build a home made bomb using these? Many possible reasons.