Here is picture of my NEF 12GA FH as it is now,
A while back I got tired of short barrel and
added a foot on to it. Used breech end of left over
Savage and a sleeve. Lined up rifling and it has
same twist and number of rifling. Hard way to do
it. No need for rifling, or extra line up work.
Run many loads and it adds 150 fps with VV110,
4759, and 4227 powders. Adds about a 100 with
Blue Dot, and HS 7.

Next one will be done different and easier.
Next one will be a smoothbore add on piece of
groove diameter, 10-12 inches long, make it one
piece, 1 or 1 1/16" threads,about 1.2" diameter.
Threaded 1.5" long on original barrel, and into
add on piece, and will look like a brake and you
could put in internal brake in the end.Ed