That's an interesting thought but not so sure it would sound the same as 1 shot. Double tap shooting is something that requires training and practice. It's not a skill everyone that shoots has. Will be interesting to see if this comes up in the defense strategy. If so, we should hear from trainers, friends or at least someone from the gun range of his ability to so.
Just been doing some research into "double tap" and watched some YT videos about it. It is a shoot to kill technique, first shot to immobilise second to kill. Special forces always use it so that a terrorist won't stay standing to shoot again after a first shot. You wait for (it is a fraction of a second) for the gun to rebound back to original position you first fired, which unbelievably it does, and shoot again. It all happens so quick. I now understand what Mangena meant when he said he would expect if OP had fired with a double tap both shots would have hit around the same area and if he fired two double taps, then all 4 around the same area. And it could be very important because OP is claiming he only wanted to scare the intruder which is why he shot low, so if the defence use the double tap explanation that would be contradictory as it means he probably did mean to kill whoever was behind the door, and in which case the prosecution has their "intent" for murder to stick. jmo