Searching for book

[Nick]

(sorry, it made me pick a book title)

So, I've been trying to tack down the name of a series I read in middle school, 25 years ago. Details are sparse, and searches so far have been in vain. Here's what I know/remember.

1. I assume YA sci-fi/fantasy (middle school library)
2. Trilogy
3. Set a time where technology is medieval
4. a boy somehow becomes king (that narrows it down right, lol)
5. Throughout course of book the council shows boy/king/etc how to make guns for his troops to win a war. it is revealed this is a post apocalyptic setting. This is 100's or years after a great war destroyed everything. Council has knowledge of technology but hides it from rulers. Once guns are made boy/king is instructed to clean up bullets and/or any evidence of weapons

Not a lot to go on I know, but this has been bothering me for years. I'd like to have these on my shelf, if only I could figure out what these were.

[Saul the Heir of Isauldur]

S. M. Stirling's Emberverse series? It's medieval-ish, post-apocalyptic.

[Nick]

I wish, but those were written 2005 it looks like. Series I'm trying to track down i read in 94(ish)