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.
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.
Going straight Louis and Clark.. I can dig it. But also ignore all that if there is magic learn to be a mage and alchemist and you can make beefed up magic powered weapons.
You can't really presume that the normal laws of physics work in a fantasy world and/or that magic can't easily transform or deflect both high speed flying pieces of metal and high-speed high-pressure gas release.
(For all you know, the greatest combat edge in that fantasy world is the speed and precision with which one can imagine things).
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.
You might be to essentially use your modern equipment as a store of magic, though. Let's say a 7.62 round takes a minute to produce magically, you now have a machine that can send the output of 10 hours of magic downrange in 1 minute. Even assuming quite a lot of loss, that could be potent depending on how your universe works.
If you know how your equipment works and can find the right smiths, potionmasters, etc you could essentially be carrying the templates for the most powerful items in the realm. Or useless wunderwaffe.
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!