I would recommend looking into Falcon barrels and doing some research on "accurate" patinball barrels before starting this, you might find the information you are looking for there and then decide if you want to try this or not. That is not to say anything here nor there about it (I've been thinking about adding something like this to my build as well, but my project is on hold for... a while
), but there have been ported barrels in paintball forever, and a ported paintball barrel witha flatline will probably give you a good idea of what would happen in airsoft.