It probably will shoot, but I doubt that the chamber is for a 3 in shell. Don't forget the lips of the hull still have to open up and any restriction will cause pressure to rise. You can get a chamber gauge that will show the length. Then you have the ejection port length and possibly the feed latch timing.
I would stay 2 3/4”, I had a nice 20 ga solid rib model 11 I should have kept it.
