I believe your gun started as a pin-fire, from the starburst detailing at the breech. For details on a complete Lock Fast, and I believe images of others if you have time to look, there is the pin-fire game gun thread. Here is a link to my Lock Fast gun in the thread:

https://www.doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=575813&page=13