No real downside that I can think of....you have the option to use 3.5" shells if required but can shoot 2 3/4 or 3". Kind of the best of all worlds. Can't see the point of owning a 3" gun if you have the option of getting a 3.5".
Totally unnecessary in Canada. Only required in the southern States after a long season of ducks becoming educated all down the flyway and staying a long way out from anything that looks like a decoy. And then only if you have the skill to hit birds 60+ yards away.
I can't recall the last time I used a 3" shell while duck hunting. Goose, sometimes if they keep away, but 2-3/4" kills them great over the decoys.
Oh, and 30" would be appropriate on the trap field, less so for skeet or sporting clays.
Well, truth be known, I'm the type that will pay to have the convenience to not have to buy another firearm
3.5" guns usually cost more, semi autos are harder to cycle target shells where thats all most use it for, Most also wont spend the $35+ per box of 3.5" 12ga shells.
Which ones are fussy? I know some of the low end autoloaders can be but we do some recreational shooting with quite a number of people all with 3.5 autoloaders and I've never seen one not cycle save for a Super Vinci and that is attributed to stance and the way the gun is held....kind of a weird thing with them. Once you learn to hold them properly the issue disappears. This issue is not unique to the 3.5" Super Vinci but also in the 3" Vinci.
I've never seen a properly maintained SBEII, A400 or Maximus not cycle 2 3/4" rounds....it sounds sporadic enough in your case not really to be a trend. Perhaps a problem with an individual gun or with maintenance. I was more looking for a pattern of several misfeeds with several different guns of the same model.



























