As mentioned, it is common to find M44's with a counterbore.
Ironically, just beacuse it's counterbored, doesn't mean it was shot a lot. It means it was cleaned a lot. What do sergeants in the field have soldiers do when there's nothing to do, or right after action? (If the area is secure...) Clean their rifles.The cleaning rod for the Mosin Nagant was made of the same steel as the barrel, and were mostly cleaned from the muzzle, (it was not long enough to go through the receiver also) When they were re-arsenaled in '46-'48, worn barrel ends were counterbored to eliminate rifling worn down or smooth, and any rough edges, then lovingly covered in layers of <sniffs> ah, cosmoline, crated, and stored in old salt mines in the Ukraine and various other parts of the soviet Union, ready to defend the rodina.