Originally Posted by
Aru
To impress the natives into believeing you're a wizard or something all you'd need is something which makes light and something which makes sound. The stuff they have at concerts. Nothing fancy, don't need Pink Floyd quality, your local pumpkin festival stuff would do. You can find solar powered batteries to make it work and bring a manual to fix it all and some spare parts. You'd be set to make magic for a few years at least. Use some imagination, hide the tech in the bush so it's not obviously technology. People were ignorant but not stupid, they would eventually realize all you have is devices anyone can learn to use, unless you trick them into thinking it's supernatural.
Of course, if you do that, you're bound to have church around your neck.
Few problems:
You wouldn't have enough raw meterials to make iron, nor coal to fuel the steam engine. Mining was primitive and fulfilled a rather low demand (due to everything being hand crafted).
Say you build a more modern iron and coal mine, with tracks, trains and steam water pumps, to fulfill your needs for resources. What would you do with all the iron you produce? Demand was low due to, as I said, small manufacturies and forges where everything was hand made and slowly made. Your iron would be much cheaper than competition, but you can only sell so much, certainly not enough to pay out the huge investment, and you can distribute it over limited area due to primitive way of transport. Being near a navigable river or sea coast would help, but not too much. Sending a ship filled with cheap iron on a weeks long journey would still cost too much, raise the price of your iron too much, the people at the destination port would still find it cheaper to buy locally mined iron. There is a reason why long trade routes carried exclusively luxury resources and stuff, and iron wasn't luxury for thousands of years in medieval period Europe.
The problem of distribution remains whatever you build. Modernish factory of whatever with assembly line, modern farming techniques, doesn't matter. You'd be able to serve only limited local region and you'd probably end up with either huge production surplus or ridiculously low prices of your goods.
There is of course a matter of pissing off all other local producers/guilds who'd gang up on you and a matter of people wanting your machinery for themselves. Your rifle would protect you for a few days at most. From what, 14th century or so in Europe, it would be recognised as very advanced hand cannon straight away, and before that it would shock people for a few days at most before they'd figure out how much damage it does, how often you reload and what it can't penetrate.
The best bet for a good living in medieval times would be actually to keep a low profile. Show up somewhere you know there is some luxury resource, gold, silver or something, which is easy to mine but still not discovered in that period. Bring something you can use to buy that land and set up mining operation using mostly medieval tech. You don't want to produce too much or be noticed for anything odd. You would live quite comfortably.
In fact, agriculture is even better bet. Simply modern agricultural techniques will let you outproduce anyone with less work than they do. You'd get comfortably rich quickly. If you really want to be seen as blessed/wizard/holy man just bring modern seeds. When they see those huge vegetables they'll be convinced you're blessed by God and as long as you don't claim to be a messiah even church should let you be.