Quoted:
So it really is true...
The bullet is completely destroyed by the blast before it gets through the target.
Either that, or it becomes a very high speed piece of shrapnel!
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Not necessarily. Depends on the projectile. Reactive armor only works on HEAT (Monroe effect) rounds.
In my HE air rifle pellet experiments, never did I see 100% breakup of the .177" pellets (including Cro Magnums). Contact with aluminum cans full of water showed about 1/2 the pellet remains as a conical projectile and thus, usually penetrates BETTER than the plain hollowpoint. The frontal nose is shattered into countless frags from vapor to small, DANGEROUS frags. A 3/4" hole is made in such a can with the metal displaced to the outside.
Back to Tannerite, depending on bullet construction, it could completely penetrate the target without much deceleration. If the velocity is high enough and detonation is delayed until the bullet is completely buried, it will see only a minimal velocity loss.
A varmit bullet MIGHT be stopped but a M2, not likely.