Aaahh yes, the patched ball...

I have the patches from the first few rounds my father fired through his custom squirrel rifle.
That thing's beautiful, it was made at the Thompson Center custom shop, it was finished just before the place burned to the ground.
The barrel has the most beautiful high polish blue job I've seen on a gun in quite some time, the wood is unbelievable.
That little thing's a small bore gun, and the patches are for the most part fully intact.

I'd figured this gun with it's much greater bore would punish the lead and somehow deposit the pains of said labor on the bore. Thanks for the note there.

I'd been looking at musket loads too to compare bore/bullet weight/powder charges. Most things seem to point in the 75-90 grain neighborhood.
Tonight's my night to do volume/weight comparisons between the fired cartriges I have from this gun and the powder measure that came with it.

My plan with the metallic cartrige design is to look at the Sharp's patents, study what pinfire hulls I have here (ten or so assorted hulls, most unfired) and consider overall volume and bullet seating issues in my initial drawings.

I also have some concerns about gas sealing in the chambers. With paper hulls, like those this gun seems to have been built for, the casings essentially 'inflate' and swell during the time of combustion. This action tends to be enough to keep, for the most part, the pressures of combustion from escaping through the breech end of the gun.
Brass cases are typically designed with rather thin case walls in comparison which have little trouble ballooning out to seal the chambers during ignition.
If I build brass case walls thick enough to emulate the shape (and so also emulate the volume of...) of paper hulls, I may end up with a cartrige that is too rigid to deform enough during ignition to seal properly. Or I might not.

So far, the design notions I've come to over discussion with my closest associate here at the shop is to build the cases in a two-part process.
This is to make the interior of the case head and webbing of the cartrige easier to machine (long reach + skinny cutters = tool chatter) and more economical in the long run as I won't have to spend much machine time or material on boring the bulk of the powder room of the cartrige from solid stock.
The case heads will likely be made from 316 or similar stainless and the case walls from brass, the pieces silver brazed then finished after brazing.
Stainless for the heads so it won't anneal during brazing, and brazed instead of threaded for greater durability. We're thinking of running a removable primer pocket and a nice little tool to make repriming easy.

My thoughts on wall thickness and interior architechure have been 'run it thick and have relatively straight interior walls, easier to run wadding if necessary'
I've also thought of running a slight hemispherical (hemitauroidal might be a better way to say it) seat ledge near the mouth of the cartriges to allow the brass to support the seat of the balls against the rifling, I wouldn't expect a thick-walled cartrige to stretch, especailly at the relatively low pressures expected with this rifle.

Much to consider really.
Still at this point I'm doing some homework on the proofs on this gun, and my proof book has gone missing. I'm feeling rather dead in the water without it, but really, the standard guide of proofs is often not nearly enough information for the stuff I end up looking at.
Someone should have a few pages of proof marks images on a web site out there...
grrr...

I may end up in the machine shop tonight turning out a couple of prototype stainless case heads, if I have the right brass tube stock, I might even turn out a couple of complete cartriges.
If I end up doing that, I'd be in serious need of an all-night testing range or soome very good sleeping pills in order to hold me over till the sun comes back up in the morning.
I have a sense once I have metallic cartriges for this gun I'll end up needing to fire it in short order just to satisfy my curiosities.
heh heh heh...