Foreword:
There might be a bit of a break ahead- I need to get my creative juices flowing.
Customs
"Single file now, no pushing. Put your wands away but have them ready for inspection."
"Said the actress to the bishops."
Agatha Longbottom sighed in exasperation as two Potters snickered. Ahead of her desk, a long line of Boys and Girls-who-lived snaked among the ornate stone columns of the waiting room. A small crater was visible on the left-hand wall where a clutch of Skrewts had escaped their crate. That particular Potter, having been raised by Hagrid, had a very inaccurate idea of the difference between dangerous animals and household pets.
"Next!"
Another Potter plunked his suitcase down onto the mahogany desk. The bowls, vases, and mugs inside rattled and slid around, but none appeared to be broken.
"Is this a pun?"
"No, I actually make pottery. Be careful though, I've trapped Voldemort's soul inside that amphora. I know some of the jars contain very angry djinni, so you'll want to watch out for those as well."
"You should be in the next room over", the greying witch said. "They're the ones who deal with dangerous magical cargo. I just check your personal possessions. It isn't my fault if you have them all jumbled together- you'll need to put the whole thing through their scan. Next!"
A Longbottom stepped up.
Agatha scanned his carpetbag, casting the appropriate charms to log the contents into the big green book underneath the desk.
"Next!"
The morning passed with agonizing slowness.
Another Potter passed her desk.
"Next!"
A particularly scarred-looking Malfoy came forward, followed by what appeared to be a soul-bonded Potter and Longbottom. Agatha scanned their trunks, and gave them advice on partitioning their minds to maintain their individuality.
"Next!"
A Potter presented her suitcase for inspection. Agatha was just about to let her past, when she noticed something unusual.
"It looks like you're carrying at least eighty pounds of steel in there. Last time that happened, your alternate had an entire forge packed away. What have you got?"
The Girl-Who-Lived opened up the case.
"What the hell kind of gun is that?"
"Don't worry- it isn't loaded."
"That's the least of my worries. What would you even use it for? I've heard of overkill, but this is ridiculous!"
It really was. The weapon in question looked like someone had taken the rotary cannon from a ground-attack aircraft, sawn off almost all of the barrels' length so that it could fit in a suitcase, and modified it to fire oversized shotgun shells.
"Well, sometimes you're hunting a legendary vampire king that eats magic, so you can't use spells against him. Sometimes he has a horde of armored thralls, so you need something rapid-fire to pierce that armor and deliver a cocktail of silver, wood shavings, and blessed salt directly to their insides. And sometimes, he's building an army beneath the Paris catacombs, so you need a gun that you can use in close quarters. The only magic is on the stock, to reduce the weight and recoil, and on the ammunition box, to duplicate the shells."
"That... actually makes sense. Congratulations- I didn't think anything could surprise me anymore. I'd say to go to the room next door, but they only deal with magical artifacts. I'll check it in, but it has to go directly into the Potterwatch divisional armory."
Agatha Longbottom sighed. It was going to be a very long day.
"Next!"
A gun is a tool designed solely for killing. Always practice firearms safety, and hope you never have to use it.