I'm making a post apocalyptic quasi-medieval setting 500 years after the fact...

A few thousand rifles stored in cosmoline probably survived, and reloading isn't that hard. They'd make a good dungeon treasure akin to a high-mid level magical item.

I mean how complex of a gun can you make without a sizable industry backing it up?

I'm doing this too. My event is the first battle of Ragnarok so all the guns and ammunition got used up in the battle thought to be the end of the world.

A single shot gun like before the yankee civil war
In general look at things before the industrialization.

>my setting is much like our world but without industrial wonders, people, their values and culture are very similar
My question to you is this: why would a pre-industrialized society have the same values as us? And which values?
Sure, you could easy say these people are democratic and believe in individuals freedoms yada-yada-yada, but I believe that their attitudes would be very different about things.
For example, without industrialization, there wouldn't likely be an abundance of surviving commodities. In our current world if say, my shirt gets ripped its not a big deal, I could go buy a new one. In a pre-industrialized society, I'd have to stitch lest I have to wait weeks to spin a new one.
Sounds like a minor change, but lets apply this situation to our perspective on sex. We are freer with it largely because of the abundance of condoms and birth control. But both latex and hormone-fixing chemicals break down over time, as does the infrastructure to create them.
You could always take the intestines from an animal, or ask the local apothecary for a herb, but a) those things aren't nearly as effective, and b) you won't have the NEARLY the same production scale. As a result, STIs and pregnancy would be more likely to occur and society's values would change around that reality.
And what about our entertainment? Most of us in the western world consume large amounts of entertainment products. We can do so because we don't have to necessarily labour for hours on end just to survive. We aren't subsistence farmers because modern farm equipment can do the job of several people in the fraction of the time. We don't need wood-gatherers or coal-miners necessarily since we have power plants and power grids that bring us our heat and light in wires.
In other words our culture consumes large amount of entertainment because we don't always have to do anything else.
A pre-industrial society doesn't have any of those luxuries.

Pretty much yes and if its post-end how bad was it? To what extent was society damaged and where. Are they still feeling the fallout 500 years later or has society gotten back enough things like standing armies and oceanic trade are back.

Think about a combination of Adventure Time and Nausicaa Valley of the Wind.

because its not a pre industrial society but our same society after a cataclysm, art and science have not been lost but infrastructure and industry have been harm beyond recovery. So simple things like traveling from town to town became very difficult because there are few cars that work and no roads without cracks.

Think of remains of technologies, buildings, etc from the fallen civilization. Great ruins of mega-polises are perhaps still there. Some pieces of lost technologies might be still functional. Some results of the apocalypse might be still there. People of some civilizations might be using some primitive electric technologies.

>500 years
Assuming everyone didn't die off in the initial apocalyptic event or physics itself didn't completely change it's reasonable to assume a society should have rebuilt itself completely after 500 years.

If argue more society has stabilized, there's a very real argument to be made we won't reach this level of energy use again if we can't find a way around it or we collapse before renewables are mature enough to make up for the eventual end of petrol.

just remember that while things fade, ideas never die as long as people don't.

by 500 years after the fact, the various vying and competing warlords have probably consolidated and are now trying to bring back whatever part of the old world they value. If the world is still medieval, it's probably a temporary state.

It could be that there's no unifying force, look at Germany for most of ever after all even late into the modern era they were a fragmented bunch of states. It may be there hasn't been a reason. To unite that petty fiefdoms have served well enough and the status quo is that for now. Or maybe an outside force is keeping things divided for whatever reason.

Well I'd go by how human society developed naturally over time. If they were blasted back to the stone age then there should be wandering tribes. If there are resources left have small societies develope around them like the city states of Mesopotamia or the greek polis. No large nations would have time to develope. So think about your resources available (food, weapons, other technology, information and administative technology) based on whats left there can only be so many developed human civillization.

I'm thinking it was likely a solar flare that caused a mass power outage across the globe and the power simply couldn't be brought back in time so society collapsed

Take a look at Degenesis. It's exactly what you described.