Anybody who has done shotgun to double rifle conversions successfully, including regulating the barrels, knows for certain, without doubt, that a properly regulated double rifle will NEVER HAVE BULLETS CROSSING AT ANY RANGE; BUT WILL HAVE bullets traveling parallel to reasonable range for caliber involved. In gunsmithing school, I took class from W. Ellis Brown, on converting shotguns to double rifles, and have successfully converted many. Brown has now written a book on this very subject, now in its second edition. All this is covered in his book. If you seriously want an answer to your question posed here, you need to read his book, if nothing more.