What model M&P are you installing it in? Some (aka: shield) may be a bit tougher than others and require more patience. Personally, I don't recommend punches for installing sights. If you are putting night sights on, I've had manufacturers tell me they won't warranty failed sights installed using a punch. There are generic pushers out there for $50-100 that work and will also allow you to adjust sights to point of aim.