+1 on practice, practice, practice.
Under the stress and huge time constraint of an "incident" where your life is on the line, you're not going to notice any difference between a few grains of powder, or a slightly lighter bullet, or whatever. And you're certainly NOT going to care if it was close to the factory stuff or not.
Sure, you have to practice with whatever loads you're going to carry, to make sure that your gun will consistently FIRE them without any problems. Shooting only one or two rounds of something is not an adequate test for your gun. You have to shoot hundreds of the same ammo/load/configuration/whatever so you can be 100% sure that your gun will fire/cycle 100% of the time.
During a fire fight is NOT the time to realize that your gun jams on this ammo every 3rd round.
So, while testing the particular loads you're going to feed your gun is important...
What matters most is that you practice w/ the same GUN you're going to carry. Your muscles and brain will remember your gun, and how it operates, and how it feels, so that when you're using your gun in self defense, there is no real "thought" involved. Only your training and natural automatic reactions.
So, as long as you carry the SAME weapon that you practice with the most, and you know your gun will reliably feed/eject/load the same ammo 100% of the time, you'll be ready and confident in your carry piece to do its job if the SHTF.
This belief in my gun/ammo saved my life not too long ago.