I actually took a standard t-handle reamer and turned it down to .454". It ran hot nd sloppy and did not produce a clean result. I actually fixed it by grinding angles onto each flute by hand; this caused it to cut cleanly and much more uniformly.
Having figured these things out I remembered that I had an extra cylinder from previous project tucked away on a shelf and started over- with much better results this time! I actually produced a workable cylinder fitted to the Kirst gated base-plate from another gun. I'll need to buy and fit another conversion ring (or make my own) to finish the gun but the gun is now functional enough to test.
The chamber walls are awfully thin between cylinders, but no worse than I have seen on period conversions and this is not a particularly potent round; the original 'Army' load was a 225gr. bullet over 15gr of FFFg, yielding a muzzle velocity of around 650fps and 207 ft/lb. I'll test with a super-light load of a 200gr. bullet over 3.0gr. of Trail Boss initially. This should give about 550fps. from this gun. If the cylinder survives that I'll carefully creep it up a bit.
If this survives I'll probably buy another cylinder and do this again. While this one will work if it is strong enough I am not best-pleased with the craftsmanship. In the meantime I'll test this one and if all goes well it will be time to detail-strip the gun, polish the cylinder and do a full refinish.
I made up six dummy cartridges to test the chambers, feeding port etc. by the simple expedient of turning down the rims of some .44 Special cases. I'll actually shorten the cases for the 'live' cartridges. Anyway here's the work to date (shown with the Pug's breech-ring.)