Okay then, far from giving up, I have more slugs to test but since results were mediocre with Brenneke'ized Lee slugs I thought I'd try full bore slugs this time.
Unfortunately I ran out of hard felt so used one hard felt disk on each and one punched from fairly firm felt insoles I had. These are punched with a 3/4" gasket punch along with a thin polyethylene disk (a little too thin but all I've got). The assembled slugs were stood up in a melted bath of my home made lube so the felt would soak it up. The idea being both to lube and firm up the felt.
Pic attached.
The TC slug has turned in not bad accuracy as an HB slug so I filled the cavity with hot melt glue then chucked in my lathe and drilled through for a number 6 wood screw. Felt and polyethylene were center punched in a jig then installed with the whole works in a piece of 12 ga. barrel so they are lined up. Stood in the melted lube then pushed through the piece of 12 ga. barrel while still hot to "size" and form the felt.
The Nessler Balles are made from a drawing of an 1800's Nessler ball as close as I could make the mould. Coincidentally (or maybe not) they came out the same weight as a bore size round ball! This "coincidental" weight makes me wonder if Nessler Balles were swaged from round balls. That would actually make sense but finding much history of Nessler Balles... well... Maybe if I searched in French/Belgian?
Some Nesslers shot very well as reported in the 1800's but then I'd get wild fliers too so overall not a success but I figured they may be on the edge of stability. Proportions are very similar to a Lee 7/8 oz. slug except the Nessler is bore diameter. With an attached tail wad maybe things will improve. We'll see. These got the same treatment as the TC slugs with filling, drilling and screwing.
Got 10 of each made up so will load and shoot shortly.
Longbow