can it be done? I want a tighter pattern but still want an 18 inch barrel. and getting a new barrel is out of the question.

Many years ago I had it done to a 870 riot barrel for rem chokes cost me 25 dollars I think its is up to about 50 now. Back then there were lots of gunsmiths advertising in shotgun news doing such.

Worked out great.

trashcanman,

Almost any 12ga barrel with an OD of over .805" at the muzzle can have tubes installed.

Check you PM for more info.