Always missing from the internet discussion boards on this topic, is the part where the original poster is (supposed) to say, "I have spent the better part of the last year patterning my (insert brand name of gun, here) with this (type of ammunition, here) and have discovered a problem, that can't be resolved by using (insert different brand or type of ammunition, here).
Why does it always go this way? At no point was it noted by anyone to start there, to see what he had.
To the OP. if your gun ended up with 2 3/4" chambers by accident, that is too bad, but, not insurmountable. It seems your notions of what to use in the gun, for the shooting you do henceforth are sound. A little testing will go a long ways, I assure you. Patterning guns is about as dull a past time activity as one can come up with, but, one that carries huge dividends, later.
I have had exactly one gun that I couldn't get useful patterns with, at typical ranges I shoot at, with ammunition I had on hand. I honestly believe I would have, but, sold the gun before I did.
Carry on.
Best,
Ted