I cannot speak for DA's in jurisdictions other than my own.. I cannot speak for how police investigations are conducted, except in areas where I have worked..
The load on the firearms examiner is HUGE, the work load on the Medical Examiner is HUGE, the Homicide Division, each investigator has at least 80 open cases EACH that demand his/her time...
In the case of an obviously justifiable shooting, the paperwork will be done quickly, the evidence given a cursory look.. The Crime scene guys will get what they have to get and move on.. The gun will be test fired and the ballistic data (the rifling imprint) will be entered into the system and it will be checked to see if it comes back a match in any unsolved shootings, it will go to a grand jury in about 90 days, and when the no-bill comes back, you will get your gun back... The type and origin of the ammunition will be a non-point...
However, if there are problems with the case, and it turns out to be a homicide, or a "who dunnit" then all bets are off... and they will crawl up your butt with microscope...
I have carried hand-loads for most of my professional carrier.. There have been, years ago abit,, several officer involved shootings with hand loads.. there were never any issues.. except in one case, the firearms examiner, and the ME could not believe the amount of damage that was done by a .380. They wanted to say that the officer was hiding another gun, or there was another shooter, someone with a 38 super or a .357.. We settled that issue (it's in the Sierra manual), provided them with the same rounds, and that was that..
But what will happen on a case by case basis, and in other jurisdictions, or in related civil matters, is a whole different world....
Personally, for my service loads, I use virgin brass, no multiple tool marks, and less concerns over contamination. I use bullets that are found in commercial loadings.. I stick with the parameters of published load data.. no wild A** Nike Zeus rounds...
If it is a concern for you, don't do it... My old department now has a policy against carrying hand-loads, probably came down from legal, but I know for a fact, that there were some problems with hand-loads on the street that failed to fire, or were grossly underpowered, and there were function and reliability issues.. In other words, there were no guarantees as to who loaded it, experience level, what they did, cleanliness, freshness and stability of components... etc...
My suggestion is, that if you have to think about it,, DON'T... find some good factory ammo, test the heck out of it, if you find one that will, function, is accurate, and with acceptable terminal ballistics,, carry that...
Understand, that lawyers, be it civil or criminal, are going to latch on to ANY moot point that they can find to try and shift blame OFF of the crook and his actions, and lay it on the blood thirsty homicidal gun totin maniac that had the audacity to protect themselves, when they know darn good and well that that the the Governments Job through the Police Department, to do that for all of us.. Unfortunately, they will grab and any straw they can to make it look like you were out for blood.... and that the fight/confrontation was totally your doing... Especially in a Civil proceeding, their job with be to make the assailant look like a victim...
I thank God I live in Texas..