I've been working on converting an out of spec No.1 action for use as a .410.
While the project's end product itself is more a sporter subject, the existence of the military .410 not only suggested the idea to me but any usable information on such a conversion would almost have to come from study of those old conversions.
So far I've taken an out of spec No.4 barrel and trimed and reshaped its shank to screw into the No.1 action. They are 180 degrees opposed so I'm setting it back half a thread. Thread pitch is the same, though thread size (dia)of the No.4 is a tiny RCH less.
The barrel is much thicker and has no crosspin cut so boring it out should leave a good sturdy .410 bore tube.
This will be chambered for US three inch shells, and I hope to make it a three to five shot repeater by modifying a DP only mag to a shorter form with single stack feed lips formed from the body of the mag better suited to the cylindrical hulls. Some work on the feed ramp will probably be necessary.
Anyway my main question is, how were the original barrels produced?
I've heard they were rebored 9.6 or similar odd size single shot rifle musket barrels from some captured enemy equipments. Some sort of Rolling Block action was mentioned.
Information on the barrels of unmodified conversions might help my project, as would any modern source for a .410 barrel made to fit the No.1 action.
BTW
I'm not converting a Drill Rifle its a discount store surplus Lithgow rifle which proved to have been rebarreled too many times and won't take a standard replacement barrel, I've tried that route.
Action is okay except for worn away , or crushed, receiver ring front surface and excessive headspace even with replacement bolt on the old barrel which had a very rough leade.
Pics below
Shank hand filed to No.1 configuration set back slightly for thinner .410 rimm by grinding the bulkhead a bit.
Breech filed to set back just shy of half a thread.
fitted to within a few degrees of clocking in by hand. A hair left to allow it to torque down solidly.
Still have to bore out the barrel and chamber to .410.
Got a couple of new projects on the fire so this one goes on the back burner again.