TOGSolid said:
Except that the only thing that the gun itself does as far as "accelerating the shell" is just to ignite the gunpowder and then off the shot goes down the barrel. Shotguns are smoothbore weapons so it's not like there's gonna be a whole lot more going on besides that. Sure, you'll have the choke at the end that will alter the pattern, but there isn't any voodoo that goes on with accelerating the shot. Longer barrel = more velocity = tighter spread = long doubleguns have the advantage.
The issues with the barrels being slightly offset isn't that big of a deal and easily solved with a bit of practice. It's not like it's going to send the shot flying wildly left or right (or up and down depending on what sorta side by side you've got). It'll just be offset by an inch or so.
The big difference is the fact that a modern pump action/semi-auto gun is going to have a lot more going on with recoil reduction and sustained, repeated fire. If modern pumps/semis were really that good, competition trap shooters would have switched to them by now.
I was about to launch into a similar response, but it seems you have done all the hard work yourself. Good job.
As you say, having barrels that are offset or above one another is barely, if at all, noticeable. The spread of the shot will cancel out the small distance between the end of the barrels anyway. Not sure about slugs though as I've never fired them but I get the impression they are mainly used in single barrel guns, so it makes no difference.
As far as accuracy goes, chokes can have a pretty severe effect. The difference between shooting clays with 1/2 choke and then 3/4 or full choke is pretty noticeable in my view. Or maybe it's just me being a poor shot and relying on wide chokes to hit stuff
Croix Sinistre said:
my personal shotgun, with rifled slugs

Stoeger 12 ga. coach gun
Nice, but as a traditionalist, it pains me to see black furniture and chrome barrels on a double barrel shotgun
Ahh who am I kidding, it looks great
OT my favourite shotgun in games and films and so on would probably be the Benelli M4, better known as the M1014.
However, my fave shotgun that I've actually used is my own Bettinsoli Over and Under 12 Bore.
I also loved the Old Winchester 101 that I had.