I go through a metric-assload of 22LR, finish up with center fire.
22lr <$0.10 a round, steel targets are cheaper and lighter, less chance to dangerous ricochet. One of those 22lr speed loaders for the MP15-22, and I don’t cringe when my kid does a mag dump. I know its not ‘cool’, but going to the range and dumping 500-600 rounds in an afternoon and working on transitions and splits, uhm- good.