Rudybollo,
I think I missed that your gunsmith rifled your barrel. Some of these rolling blocks were produced with rifled barrels and were marketed here as 28 ga. I use 8x50R Lebel cases in my 12.7x42( Belgian Cape gun), but they are too small for your gun( they are listed as .536"). The 577 snider is listed in the often mistaken COTW as .660" head diameter, and .577-450 as .668". Rifle cases will be thick enough to allow a little reduction in diameter by turning, or swaging. BTY, I don't think is weird.
Mike