My blacksmith living next to the Starport with 1500 technology enjoys a successful trade in matchlock arquebus with about 25% of the local Army being equipped with one. So when he becomes friends with the Engineer and they get to talking, he already has a good foundation to build on and is fascinated by the pictures on the HandComp of how a flint lock works. He tries out the pump action shotgun, and my INT A Master Blacksmith immediately sees how he can incorporate improvements in the design of his stock and is fascinated with the idea of creating paper cartridges. He lacks the tooling to make a working percussion cap weapon, or a real bullet, but any number of modern improvements might still be incorporated ... Even as he struggles with some experimental TL 3 prototypes.
L. Sprague de Camp, Lest Darkness Fall. A great read!