I've been reading the posts on the accuracy problems with .44 mags. I have an unfired barrel that has been kicking around my shop for years and just from curiosity I did a chamber cast on it and found something quite interesting. It is quite oversize at the base, .463", a long gradual taper of about 1.310" to a mouth diameter of .458". There is no throat in the conventional sense, not at all like a revolver chamber, but just a short taper .135" long from .458" down to groove diameter of .432". I wonder if that may explain why rechambering to a longer cartridge often seems to improve accuracy.
Certainly the oversize bore and slow twist are problems but I suspect this chamber design may also be a factor. At any rate, this barrel is likely to remain unfired.