C-, problem is this caliber, as well as the .444 are restricted and mostly unknown here, as magtech AFAIK doesn't load them and it's the only ammo maker one could buy restricted ammo and components (and black market for these two I guess is not that hot... LOL). Just a weird curio you all may not know: Would you believe possessing an ammo component like fired cases is considered a felony by the law if you don't have the papers??? (of course they would need to get you with them or have a warrant to search your house).
After slugging the bore I got somewhat frustrated, but after finishing some chores and taking a shower, I got some ideas... can't say if they are feasible for now:
1) copy the hornady triple defense load (which is not available here) concept: a hollow base slug with a ball pushing the skirt outwards. Hopefully I can copy Uncle Dino's stacked buckshot die (and have a machinist make one for a little sum) to swage such slugs...
2) copy the british webley .455 hollow base bullet in some way, hoping the mass forward is enough to stabilize such slug and the base expands to fill the bore.
3) stick to duplex ball loads, assuming the neck loading attempt works and forget about single projectile loads.
4) think about something else and if all fails, sue taurus for selling an out of spec product. If we can't have the .45Colt shooting ability, they should at least bore the thing to meet .410 only dimensions and tolerances. While I'm not sure of the success, probably we can settle an agreement or something.
I really don't want to give up this gun, because the other options would be .38spl and .380 for which I can't reload (you know, the army permit stuff et al).
left row: 9x3/8oz mixed birdshot loads (#8 to #6), then 3x3/8oz BB shot loads (just to pattern the gun which I didn't yet). center front: 4 neck loaded 2x ~.43" balls. right row: 1x ~.43" round ball, seated like shotshells, then 5 neck loaded 2x.40" balls (marked 2*4).