Yes flintfan,
That's what I mean.Actually I think its not in front of the chambers...but that that those turned down inserts run from just ahead o the chamber right down to the shell rim cut at the breach end...the shell rim must have to be re cut , as its either partially or totally gone because of the boring job...and you will have a least some unfinished bit of the new tubes stopping flush with the end of the original chamber wall....right....????
Or put another way...how thick in the wall is the reduced insert part of the new bbls,in a percentage of the finished breach end chamber wall???
Know what I mean?
Cheers, franc