For useful definitions:
http://www.hallowellco.com/lumps.htm

This gun uses a mono-bloc


These barrels were fabricated to make chopper lump aka demi-bloc


http://www.doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=45466&PHPSESSID=
Originally Posted By: 2-piper
I count at least three methods which allow the bbls to be set as close as the chopper lump.

1-conventional;
2-dovetail lump;
3-shoe lump.

Closness on any of these is limited only by the amount necessary for regulation or the strength of the matl, whichever comes first, same with the chopper-lump.


Pete

http://www.damascus-barrels.com/Movie.html