Question on bullet grain and SD?

I recently got a Glock 19 Gen 5 for home defense and soon to carry. I've read the FAQ and done some searches but I had a few remaining questions regarding SD ammo.How does differing grains affect shots in terms of wound creation and follow up shots? I've been reading that 124g is the most accurate in G19s or that 147g has less recoil, etc.Folks say to use bullets that the FBI use for legal defense. I'm curious why that is and how what kind of bullet you carry affects legal arguments for self defense?I ask since I'm deciding between Barnes 115g TACXPD, Federal HST 124g and Federal HST 147g. I'm not concerned too much about the brand but more so the grain and +P or not to +P. via /r/CCW http://bit.ly/2RigMx5