Quoted: You have to buy the MARK XIX to be able to interchange calibers. MRI website--www.magnumresearch.com/products.asp

Not really, since the difference between the models is the slide and barrel thickness, and a MK VII in 50ae is really a MK XIX since it already has the thicker slide and barrel of the MK XIX.

So, if you picked up an Mk VII in 50, then you could go to 44 with a MK XIX barrel, then 357 with an Mk XIX barrel and bolt (will still need the new mags).  Now if you have an Mk VII in 44, then you can still go 357, but will need a MK VII barrel to go with the thinner side.


Bottom line is the MK VII in 44 and below had a thinner slide and will not work with the Mk XIX barrels. The MK VII in 50ea required a thicker slide for the barrel, and what started the new series (New 44 and 357 barrels to fit the thicker 50ae slide).