Those 'first' ones by "BRI" were the same as Winchester and Federal are still selling today. The do require a twist of around 30" or perhaps 28", as the normal rifled 12 bore 36" twist still yaws them at 50yds., badly. There is generaly a figure "8" hole, instead of a perfectly round one.
; The standard Foster slug is still the best in the smoothbore, with it's solid nose, and HUGE hole in the back to give it a shuttle-cock effect. A wind sock is sort of the same idea. BTW- The grooves on the sides or a "Rifled Slug" DON'T spin :bull: the slug in the air as they are mostly smashed smooth by the bore, and there is a solid rib around the back end, anyway, to cut off any air in the remaining groove that might be trying to spin them. - TRUTH!
: I considered the Lee mould of the Foster type, but cross-keyed for strenght, but because of the design, the mould is not easily modified in size or to thicken the skirts if required, so I never bought one. I did, however make up an adjustable mould that cast a 580gr to 1,200gr. HB slug for the .69 rifle that was a success. This one looked identical to a foster slug from a Lyman mould, but only cost me an old mould no longer used. I re-bored it with a modified 11/16" drill and made up a plug for the hollow base that made for nice thick skirts. Due to the shank being the full .687", and when rolled with a wood rasp on towels, it gained in size to .692" with lots of cuts for lube, it was adjustable to 1,200gr. from a low of 580gr. With 8 second re-loads using paper ctgs. and round balls, I didn't need the slug for a fast second shot, but the light 580gr. slug, shot to the sights to 50yds. and was as accurate was RB due to it's being very short, barely longer than a round ball. I stayed with the round balls and paper ctgs. as they were more convenient and faster to load.
: Big slugs are really cool & fun to play with- especially at 1,00gr. or more - the only problem with the waisted ones is to maintain integrity when the powder charge goes off(the waist might collapse irregularly) and the skirt has to be thick enough to not blow out & rifling twist fast enough to stabilize a bullet that long. After that, it's all gravy( & recoil!