well I have a few questions just to know, not bashing
BUT HOW are you test firing this gun?
are you using a good solid rest.sandbags, ??
are you taking 3 shot groups, 3 large sized targets, many warehouses can get you 4x4" cardboard for doing this pretty cheap)
and don;t laugh its can show you more info than one shot them move and another, kinda of like a rifle!
are you using the basic bead sight on the barrel?
its is NOT that uncommon for a bead to be off, causing a gun to shoot high,low, left or right
but should still be consistent, in what ever direction it us ending things!
when things are , it can be due to a few things, from a loose barrel on the action, a burr on the end of the bore/muzzle, too tight of a choke, a burr where the choke fits too the barrel
and even a bent barrel, but I have seen VERY few bent barrels over the yrs I had a gun shop, and been in this sport, but never say never!
what you need to do is rule things out here
make sure barrel is tight to receiver
once on tight, grab and see if there is any movement in things !
if none?
check/inspect the chamber of the barrel for any burr's, or anything that might cause the bolt not to close completely. there are not rifles with super tight tolerances, there is more wiggle room in a shotguns chamber and bolt face!
using a camera if you can take pic's of things, upload to a good PC and then be able to zoom in and see things the naked eye might miss,,
to rule out too tight a choke, try an improved cylinder, just to see if things GROUP, all high/low/left/right
if so, then you know its in the chokes
if not, you again, can take pic's down the muzzle end of barrel and again, use a PC to zoom in and enlarge things, to maybe see smaller details your eye's will miss
if nothing is found,, IMO< you can either contact Winchester, have them either send gun back, or take to an authorized repair center and have inspected, or corrected
OR< plan B< can always TRY another barrel, if you can find someone with one, and or BUY one? not a cheap option at all, but is an option!