2 3/4 followed by 3” Invector    Pretty sure it says Invector.  Is that gonna blow me and the barrel up?  Just kidding.  Maybe.  Guessing it will shoot both.  I tried finding a definitive answer, but I didn’t get quite the knowledge that I think I would have found here.  Gonna be taking it with me in the morning for turkey hunting.  About the third time I’ve been and have been using my trusty 870 Wingmaster, which I’ve had since the mid 70-s.  I’m gonna try to get some sleep before getting up at 0420.  Every time I go, the night before seems like Christmas Eve to a child,  so that may be difficult.  If I don’t answer any questions forthwith, I’ll be checking/responding too them in the am. Thanks for any info provided.

Invector is brownings brand name for their choke tubes.

I’m guessing the chamber is 2 3/4, but it needs 3 inch choke tubes.

Don’t know if I can find those tubes.  Pretty sure some came with it.  I’ll just use the 870 till I do.  Thanx!

Is the barrel marked something like this:            2 3/4” - 3” Invector   ?

Is this the old style steel receiver "humpback" A5, or the newer inertia operated A5?

Yes, the newer inertia one.  Says 3" Invector DS-28"

You can shoot 2 3/4” or 3” shells in that gun.

Invector DS is the type of choke tube the barrel accepts. (Invector DS tubes are NOT interchangeable with Invector or Invector PLUS tubes)

Thanks.  Breathing easier!!