After seeing the pics of a Greener 12ga double in Rifle magazine, I've decided that someday down the road I'll have to have one. Barring buying one of the old masterpieces, how feasible is it to buy a 'modern' 12ga smoothbore and have it rebarreled with rifled barrels (1 in 9 foot twist or so) for shooting roundballs? Is the rebarreling, regulating the barrels and installing sights more expensive than shopping for something with history?? Thanks for any and all information.