Gun Digest‘s Grant Cunningham writes: The idea behind the +P is to add enough energy to reliably deliver an expanded bullet deep enough to do its job. It doesn’t have to be a lot of extra energy – it just has to be enough. Here’s what you need to know.
What About +P Ammo?
Remember that hollowpoints use part of their energy to expand their diameter, but the energy that’s used to expand the bullet is energy that can’t be used to drive the same bullet forward. There is no such thing as a free lunch; if you want the bullet to expand, it’s going to use energy. If there is too little of it to start with, there won’t be enough left to carry the bullet on its path.