Just memorize your guns and ammos schematics and then use magic to manufacture them out of thin air. Sell them for gold and watch the fantasy world collapse due to hyper-efficient slaughter your guns brought to the world. Then come back to your original world with your metric tons of gold and watch the economy collapse as you dump your gold into the market.

The engineer: they're standing on a boat?

I cast web on the boat surface, then get the sorcerer to fireball the web, then have the wizard shatter the boat from under them.

Alt: being chased by pirates: distant metamagic a grease spell on their main sail, then quicken spell and distant spell a firebolt. No more main sail on pirate ship. DM was both impressed and sad his pirate fight fizzled.

This is the premise of that anime “The Gate”. It’s stupid, pure Japaneese military propaganda but really entertaining. To put it in perspective Dark Elves phase in and out armed with manpads vs a fire dragon!

A good option might be these high powered airguns strong enough to drop a moose. Like the .72cal Zeus, it has the same muzzle energy as an AK-47. As long as you can get your hands on lead, you can make your own ammo.

Forget which bang stick to use.

Can you take 50K of ammo back with you?

That is the real question.

Edit: Oh, and a couple of spare barrels would be a good idea as well. Actually, at least three spares of everything.

I think if magic can sustain your modern equipments, there would be a more efficient native way to utilize it. Like the energy to construct and supply bullets to your AK-47 maybe better used as rapid fireball directly.