Bearing in mind the cost of the Corbin swaging unit and dies is probably a couple of times more than the cost of the rifle, it might be an idea to make contact with Brett Gibbons - see papercartridges.com - who uses a Corbin swager to make and sell cylindrical bullets that look just like the example. It's also a plan to watch him on Youtube, shooting his Whitworth replication, offhand, and hitting steel at some pretty impressive ranges.
As many of us have discovered, that figure of .451" is a nominal diameter that is seldom adhered to. My P-H Whitworth measures .4495" across one set of flats and .4485" across the other - nowhere near the NBD of .451". It is this 'little problem' that besets many of us holding out for a hexagonal mould of one kind or another. They are NOT cheap - the Pedersoli version is around $200 and uses it own hole-spacing handles, to add to that. K.A.L in Manitoba may have stopped making theirs, at around $250 or so. And when you get them, and they are the wrong size, you are screwed, to coin a phrase [look up what Whitworth invented when he wasn't playing with guns and rifling]. It is impossible to resize a hexagonal bullet.
So, Lyman make a .451" multi-groove bullet mould, if you can find one, and also in US, NOE makes a suitable cylindro-conoidal mould to your dimensions, and Brett sells a bullet that requires paper-patching. David Minshall here is THE information source with his Research Press site, in which you can find out more about shooting the Whitworth. I recommend it to anybody with ambitions in that direction. I bought my first P-H Whitworth in 1986, and sold it in 2015 to somebody who was desperate to have one to shoot long range. I found another last year, even older and have been shooting cylindrical bullets with it so far, although I have a Pedersoli hex mould from a pal back in Canada that makes a bullet that does fit closely.
This is my best shooting so far - ten shots at 100m with 70gr of Swiss #3 with round bullets of 535gr made from a Lyman mould - it has a pointy nose and multi-grooves, and needs careful loading so as not to deform it in any way. Open iron sights and a sore shoulder from the day before is my excuse. You'll need to experiment with loads and grades of powder, just like the good ol' boys did back then.
View attachment 135664
Over on Youtube again, capandball [Dr Balász Németh], has a few videos on shooting the Whitworth, both P-H and the Pedersoli version.