My solution is to scale to the coffin which 100% either tanked the explosion undamaged, or had Alucard protect it with shadows.
The coffin also happens to be a sentient monster thing.
As for the anti-feats, it appears to be Alucard allowing himself to be hurt, either because he is a ********* or he enjoys showing off on his opponents with his immortality. He scales to True Vampire Seras and Alexander Anderson.
Seras and Anderson have no issue tanking normal machinegun bullets.