Oh, found a link to a rifle that might suit your purpose to copy or give you more ideas:
Rifle Made by John Christian Oerter - Museum of the American Revolution (amrevmuseum.org)
We actually have an original letter from Christian Oerter to a customer on what probably was a somewhat higher grade rifle. The text translated from German reads:
Christiansbrunn, the 9th September, 1773
Most valued Friend Martin Baer,
At your request I have prepared [completed/finished] a good rifle and sent it over to Mr. John Hopson together with 4 pounds of Powder. The rifle is decorated [inlaid] with silver wire and well made, as well as tested and she shoots right well. It has a double trigger, so that you can fire with the triggers either unset or set. Between the triggers there is a screw with which you can make it lighter or harder to fire. There is also a ball puller with which you can pull the ball out no matter how rusty she gets. She costs 8 pounds all together and with the powder @ 3 shillings per pound makes twelve shillings, for a total of L8.12.-. Because it is very good powder I have added two pounds more than you requested. I hope it will suit you well. You can write me a couple lines to let me know how you like it. Together with friendliest greetings I am your faithful
friend and servant,
Christian Oerter
Gunmaker
Also, here's another link you may enjoy:
The Pre-Revolutionary North Carolina Rifle - Scavengeology
Gus