You could fairly easily build a single working gun analogue, it just wouldn't be even close to the guns of today.

Though the difficulty, would vary greatly depending on the components you have to hand in the time-period you landed

The mechanism of a shotgun or musket is relatively simple.

Granted , the black powder chemistry is a bit tricky and requires intermediate chemistry steps AFAIK.

If you needed to do metallurgy from scratch that would increase the estimation by a lot.