JGS sell a reamer for long cases made to Rob's specs.
IE a minimum chamber for the thinner mouth brass.
I made my chambers with lathe tools.
Here is picture the CBC 20ga FH setup
by mono-blocking a heavy 20 ga barrel
into a CBC 12ga breech section.The 20 heavy
barrel is threaded into the mono-block made
by cutting off 12ga barrel. These CBC actions
are taller and wider than other break actions
and the locking lug block works better and
nicer than other break actions.Also shown
is 20ga 3.5" plastic and brass cases.
Second picture is PH action with port lengthened
for 585HSM, shown in action. I also have second
change barrel for 700HE long case for this action.
Imagine over 20,000 ft lbs in a PH, for 700HE.
Also shown behind is a PH with 700H 3.25"..Ed