A bad or poor crown is a strong possibility, so is the simple physics that a shorter tube is a stiffer tube. Stiffer is less barrel whip when shooting equaling better accuracy.
On my Maxi I did not knotice better accuracy. It certainly did not get worse, but not better. Just a bunch handier!

Many of us have experienced this too. You go to range and get ok accuracy or excellent accuracy only to return another day, not change anything and find the opposite has happened.
A couple common accuracy problems associated are oil/powder residue on the latch. Keep the latch shiny clean for better and more consistant accuracy. If stored butt down, oil can seep to the latch.
Another common trait, as much as I hate to admit it, many find better accuracy shooting dirty. It will get to a point where accuracy will drop off that's a given. But the so so quality of H&R barrels seem to do better with a couple hundred rounds threw them....
Good luck,
CW