I've already trashed a lot of this design but it gives you a general idea on what I'm going for.
I had my heart set on something that could throw .50 cal steel at about 200FPS and was quick to draw and load, so I cut the barrel to accomodate a power stroke of 11.5" however the prod will only be about 90lbs, as I understand, with light projectiles its the powerstroke that does most of the work rather than the draw weight. I came up with a sort of tube magazine built into the tiller similar to a Girandoni air rifle and I plan to have a little lever or bar that will trip a ball into the barrel when activated. I wanted a rifle-sized crossbow, but I also wanted something compact and portable to take on woods trips, at first I decided to settle on a short musketoon style of tiller but later I discovered some really nice flintlock rifles that were designed with collapsible stocks to be portable on horseback, so I decided on something similar.
Here's a few pieces of cherry I'll be laminating together with a red oak core to make the tiller, and the slotted barrel next to it, which looks really bad in some spots where I botched the cut (was using a small dremel tool with no sort of guiding jig), however all of the rough spots are parts that will be inletted into the stock and wont be visible in the final crossbow.
I'll have more progress to post in a few days, hope you like my idea.