Shotguns: My homily; I have been shucking shotguns since before I joined the Army at 17. Carried one for the Army. Did a branch change to the USCG, carried one there. Became a big city cop, then a sheriff. Looking at 65 years of military/LE in the rear view mirror. I am the same age as Joe Biden, however, I, can walk, chew gum and mumble all at the same time.
American shotguns are pretty much the iconic one shot defensive weapon, or two or more if needed. They work, right out of the box and pretty much forever if you have a brand name gun. And they stop, I did 46 armed robbery stakeouts with Chicago PD, the shotgun always worked when professionally applied to the problem.
Tactical observations: Shotgun slings; they are really better suited for military operations than LE/defensive use. A sling is for humping your weapon long distances or for letting it hang while in a static position. The idea of dropping your shotgun to let it hang while you deploy your handgun with a greased lightening presentation is just BS, even the SEALS don't train that way. If the gun is not working for whatever reason, just drop it, you don't need it any more. Use youir handgun or throw rocks, or use the SG as a bludgeon (it does well in that mode).
A promise; if you stalk around any area with a shotgun held at the ready, and it has a sling, that sling will foul on something, just when you do not want it to do so. The number of things that it will foul on are legion, just about anything will do, including the handgun/equipment you will probably be wearing. Sling in a vehicle? Get thee behind me Satan. Not even mentioning the handhold that sling will give the bad guy.
Racking the slide for psycho reasons: The only person that sound ever frightened was me, as in running up a flight of stairs with the new kid behind me racking his weapon (a slam firing Ithaca). The average bad guy who breaks into your home/office or wherever is simply not thinking like you and me, and he is definitely not thinking well, he is doped up, freaked out on some natural substance or just plain crazy. The sound will mean nothing to him (and yes it will be a him 99.99% of the time). I never worried about the sound of racking a SG giving away my position as it was normally followed by a much larger sound, your deployment should follow suit. Not that you should be trying to kill someone, but if the situation requires racking it will also almost always require shooting. I always hesitated for a short second in case the "sacry sound" did work, but the obligatory verbal announcement usually did. I never saw anyone surrender to the clack clack sound. Or heard of it either.
You can (and probably will) miss with a shotgun. That is why you must train with the SG/load you will use for serious social happenings. I have trained scores of folks (miliatry and LE) with the SG, they will all miss the first time out.
I favor #4 or #3 buck for ranges out to 12 yards and 00 buck for longer ranges (out to 25-30 yards), any range longer than that you should be shooting something else unless you and your gun are really good with slugs. My go to long gun is a Browning A bolt rifled barrel 12 gauge, or I also have a Remington 1100 with a rifled barrel, both have low power optics. The Browning is deadly out to 135 yards. Like 2 MOA deadly. The two rifled barrel guns have slings, they are humped a lot.
Ammo: birdshot is for the birds, literally. It will produce a large shallow wound in a large animal, that will bleed lot, but not be a stopping wound under most circumstances. And at close ranges where the wound might be useful, you can easily miss, just like with buck or slugs. Why gamble?
Loadout: Never, but never, mix loads in a magazine. Do not succumb to the idea of loading small buck, then larger buck then a slug or two. That would be basing your loadout on going from shorter range to longer range. Sometimes things do not happen the way we want them to. Never, but never, mix less lethal loads with lethal loads. Unless you like paying large civil judgements or maybe seeing the inside of state accomodations for a while. It is grossly negligient at best and criminally negligient at worst. Even just mixing lethal loads may make grist for the attorney mill. Any sleazebag lawyer will make you dizzy with questions about a mixed loadout in your magazine, been there done that, got the T-shirt.
Just my .02....YMMV-but not likely.