Bavarianbrit,
A few of us here, well myself at least, would like to hear how you get on with this...please keep us posted...
It seems to me that as you are starting with a bore with a diameter of what the groove diameter was, cutting new grooves will make everything twice as big as the depth of groove..bigger in diameter.Will cutting new grooves in the bore make it too big for the intended 20 Gauge?
Perhaps with a longer bullet with gas check (?), it might Plump up to seal well.
I guess if that wouldn't work, you'd have to get someone to bore it out a bit to re line it with a rifled sleeve done to "Normal" 20 bore rifled specs?
Just armchair theory of course, but let us know.
Let me know if what I said was right , too, ok lads?
I'd love to find a heavy walled single shot to turn into a ball/bullet gun
cheers
franc